tools/intel_reg: Don't reuse stale decoded results for later registers

In case the ->debug_output() function skips decoding the register it
just returns, which means the caller will reuse whatever it already has
in the tmp buffer as the decoded result for this result. What it usually
has in there is the decoded result of some previous register.

Showing incorrect decoded results is no good, so let's allow
->debug_output() to actually return how many bytes it wrote, and the
caller can then skip showing the decoded results if zero bytes
were produced.

We'll make a variant of snprintf() that's safe to call without having to
check the return value for the case when it didn't have enough space to
do its work, that is, make it return 0 in case no bytes were written.

v2: Document the _DEBUGSTRING() funcion (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 121 insertions, 86 deletions

diff --git a/tools/intel_reg_decode.c b/tools/intel_reg_decode.c
index 71f3ead6..c6246ef1 100644
--- a/tools/intel_reg_decode.c
+++ b/tools/intel_reg_decode.c
@@ -26,6 +26,7 @@
  */
 
 #include <errno.h>
+#include <stdarg.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -38,13 +39,45 @@
 
 #include "intel_reg_spec.h"
 
+/**
+ * DEBUGSTRING:
+ * @result: character string where to write
+ * @len: maximum number of bytes to write
+ * @reg: register offset
+ * @val: register value
+ * @devid: PCI device ID
+ *
+ * Print the decoded representation of the register value into @result.
+ *
+ * Returns: Number of bytes written to @result
+ */
 #define _DEBUGSTRING(func) \
-	void func(char *result, int len, int reg, uint32_t val, uint32_t devid)
+	int func(char *result, int len, int reg, uint32_t val, uint32_t devid)
 #define DEBUGSTRING(func) static _DEBUGSTRING(func)
 
+/* snprintf that returns 0 when the thing didn't fit */
+static int __attribute__((format(printf, 3, 4)))
+z_snprintf(char *str, size_t size, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, fmt);
+	ret = vsnprintf(str, size, fmt, ap);
+	va_end(ap);
+
+	if (ret >= size) {
+		fprintf(stderr, "snprintf() returned %d, expected < %zu\n",
+			ret, size);
+		return 0;
+	}
+
+	return ret;
+}
+
 DEBUGSTRING(i830_16bit_func)
 {
-	snprintf(result, len, "0x%04x", (uint16_t) val);
+	return z_snprintf(result, len, "0x%04x", (uint16_t) val);
 }
 
 DEBUGSTRING(i830_debug_dcc)
@@ -52,7 +85,7 @@ DEBUGSTRING(i830_debug_dcc)
 	const char *addressing = NULL;
 
 	if (!IS_MOBILE(devid))
-		return;
+		return 0;
 
 	if (IS_GEN4(devid)) {
 		if (val & (1 << 1))
@@ -76,7 +109,7 @@ DEBUGSTRING(i830_debug_dcc)
 		}
 	}
 
-	snprintf(result, len, "%s, XOR randomization: %sabled, XOR bit: %d",
+	return z_snprintf(result, len, "%s, XOR randomization: %sabled, XOR bit: %d",
 		 addressing,
 		 (val & (1 << 10)) ? "dis" : "en",
 		 (val & (1 << 9)) ? 17 : 11);
@@ -101,7 +134,7 @@ DEBUGSTRING(i830_debug_chdecmisc)
 		break;
 	}
 
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "%s, ch2 enh %sabled, ch1 enh %sabled, "
 		 "ch0 enh %sabled, "
 		 "flex %sabled, ep %spresent", enhmodesel,
@@ -114,24 +147,24 @@ DEBUGSTRING(i830_debug_chdecmisc)
 
 DEBUGSTRING(i830_debug_xyminus1)
 {
-	snprintf(result, len, "%d, %d", (val & 0xffff) + 1,
+	return z_snprintf(result, len, "%d, %d", (val & 0xffff) + 1,
 		 ((val & 0xffff0000) >> 16) + 1);
 }
 
 DEBUGSTRING(i830_debug_yxminus1)
 {
-	snprintf(result, len, "%d, %d", ((val & 0xffff0000) >> 16) + 1,
+	return z_snprintf(result, len, "%d, %d", ((val & 0xffff0000) >> 16) + 1,
 		 (val & 0xffff) + 1);
 }
 
 DEBUGSTRING(i830_debug_xy)
 {
-	snprintf(result, len, "%d, %d", (val & 0xffff), ((val & 0xffff0000) >> 16));
+	return z_snprintf(result, len, "%d, %d", (val & 0xffff), ((val & 0xffff0000) >> 16));
 }
 
 DEBUGSTRING(i830_debug_dspstride)
 {
-	snprintf(result, len, "%d bytes", val);
+	return z_snprintf(result, len, "%d bytes", val);
 }
 
 DEBUGSTRING(i830_debug_dspcntr)
@@ -139,9 +172,9 @@ DEBUGSTRING(i830_debug_dspcntr)
 	const char *enabled = val & DISPLAY_PLANE_ENABLE ? "enabled" : "disabled";
 	char plane = val & DISPPLANE_SEL_PIPE_B ? 'B' : 'A';
 	if (HAS_PCH_SPLIT(devid) || IS_BROXTON(devid))
-		snprintf(result, len, "%s", enabled);
+		return z_snprintf(result, len, "%s", enabled);
 	else
-		snprintf(result, len, "%s, pipe %c", enabled, plane);
+		return z_snprintf(result, len, "%s, pipe %c", enabled, plane);
 }
 
 DEBUGSTRING(i830_debug_pipeconf)
@@ -157,7 +190,7 @@ DEBUGSTRING(i830_debug_pipeconf)
 	else
 		bit30 = val & I965_PIPECONF_ACTIVE ? "active" : "inactive";
 
-	buf_len = snprintf(buf, sizeof(buf), "%s, %s", enabled, bit30);
+	buf_len = z_snprintf(buf, sizeof(buf), "%s, %s", enabled, bit30);
 
 	if (HAS_PCH_SPLIT(devid) || IS_BROXTON(devid)) {
 		const char *interlace;
@@ -190,7 +223,7 @@ DEBUGSTRING(i830_debug_pipeconf)
 			break;
 		}
 		if (buf_len < sizeof(buf))
-			buf_len += snprintf(&buf[buf_len], sizeof(buf) - buf_len,
+			buf_len += z_snprintf(&buf[buf_len], sizeof(buf) - buf_len,
 					    ", %s", interlace);
 	} else if (IS_GEN4(devid) || IS_VALLEYVIEW(devid) ||
 		   IS_CHERRYVIEW(devid)) {
@@ -217,7 +250,7 @@ DEBUGSTRING(i830_debug_pipeconf)
 			break;
 		}
 		if (buf_len < sizeof(buf))
-			buf_len += snprintf(&buf[buf_len], sizeof(buf) - buf_len,
+			buf_len += z_snprintf(&buf[buf_len], sizeof(buf) - buf_len,
 					    ", %s", interlace);
 	}
 
@@ -240,7 +273,7 @@ DEBUGSTRING(i830_debug_pipeconf)
 			break;
 		}
 		if (buf_len < sizeof(buf))
-			buf_len += snprintf(&buf[buf_len], sizeof(buf) - buf_len,
+			buf_len += z_snprintf(&buf[buf_len], sizeof(buf) - buf_len,
 					    ", %s", rotation);
 	}
 
@@ -265,11 +298,11 @@ DEBUGSTRING(i830_debug_pipeconf)
 			break;
 		}
 		if (buf_len < sizeof(buf))
-			buf_len += snprintf(&buf[buf_len], sizeof(buf) - buf_len,
+			buf_len += z_snprintf(&buf[buf_len], sizeof(buf) - buf_len,
 					    ", %s", bpc);
 	}
 
-	snprintf(result, len, "%s", buf);
+	return z_snprintf(result, len, "%s", buf);
 }
 
 DEBUGSTRING(i830_debug_pipestat)
@@ -323,7 +356,7 @@ DEBUGSTRING(i830_debug_pipestat)
 	    val & VBLANK_INT_STATUS ? " VBLANK_INT_STATUS" : "";
 	const char *_OREG_UPDATE_STATUS =
 	    val & OREG_UPDATE_STATUS ? " OREG_UPDATE_STATUS" : "";
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "status:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
 		 _FIFO_UNDERRUN,
 		 _CRC_ERROR_ENABLE,
@@ -366,41 +399,41 @@ DEBUGSTRING(ivb_debug_port)
 			drrs = "high";
 			break;
 	}
-	snprintf(result, len, "HW DRRS %s",
+	return z_snprintf(result, len, "HW DRRS %s",
 			drrs);
 }
 
 DEBUGSTRING(i830_debug_hvtotal)
 {
-	snprintf(result, len, "%d active, %d total",
+	return z_snprintf(result, len, "%d active, %d total",
 		 (val & 0xffff) + 1,
 		 ((val & 0xffff0000) >> 16) + 1);
 }
 
 DEBUGSTRING(i830_debug_hvsyncblank)
 {
-	snprintf(result, len, "%d start, %d end",
+	return z_snprintf(result, len, "%d start, %d end",
 		 (val & 0xffff) + 1,
 		 ((val & 0xffff0000) >> 16) + 1);
 }
 
 DEBUGSTRING(i830_debug_vgacntrl)
 {
-	snprintf(result, len, "%s",
+	return z_snprintf(result, len, "%s",
 		 val & VGA_DISP_DISABLE ? "disabled" : "enabled");
 }
 
 DEBUGSTRING(i830_debug_fp)
 {
 	if (IS_PINEVIEW(devid)) {
-		snprintf(result, len, "n = %d, m1 = %d, m2 = %d",
+		return z_snprintf(result, len, "n = %d, m1 = %d, m2 = %d",
 			 ffs((val & FP_N_IGD_DIV_MASK) >>
 			     FP_N_DIV_SHIFT) - 1,
 			 ((val & FP_M1_DIV_MASK) >> FP_M1_DIV_SHIFT),
 			 ((val & FP_M2_IGD_DIV_MASK) >>
 			  FP_M2_DIV_SHIFT));
 	}
-	snprintf(result, len, "n = %d, m1 = %d, m2 = %d",
+	return z_snprintf(result, len, "n = %d, m1 = %d, m2 = %d",
 		 ((val & FP_N_DIV_MASK) >> FP_N_DIV_SHIFT),
 		 ((val & FP_M1_DIV_MASK) >> FP_M1_DIV_SHIFT),
 		 ((val & FP_M2_DIV_MASK) >> FP_M2_DIV_SHIFT));
@@ -424,7 +457,7 @@ DEBUGSTRING(i830_debug_vga_pd)
 		vga1_p1 = ((val & VGA1_PD_P1_MASK) >> VGA1_PD_P1_SHIFT) + 2;
 	vga1_p2 = (val & VGA1_PD_P2_DIV_4) ? 4 : 2;
 
-	snprintf(result, len, "vga0 p1 = %d, p2 = %d, vga1 p1 = %d, p2 = %d",
+	return z_snprintf(result, len, "vga0 p1 = %d, p2 = %d, vga1 p1 = %d, p2 = %d",
 			 vga0_p1, vga0_p2, vga1_p1, vga1_p2);
 }
 
@@ -446,12 +479,12 @@ DEBUGSTRING(i830_debug_pp_status)
 		break;
 	}
 
-	snprintf(result, len, "%s, %s, sequencing %s", status, ready, seq);
+	return z_snprintf(result, len, "%s, %s, sequencing %s", status, ready, seq);
 }
 
 DEBUGSTRING(i830_debug_pp_control)
 {
-	snprintf(result, len, "power target: %s",
+	return z_snprintf(result, len, "power target: %s",
 			 val & POWER_TARGET_ON ? "on" : "off");
 }
 
@@ -539,7 +572,7 @@ DEBUGSTRING(i830_debug_dpll)
 		sdvoextra[0] = '\0';
 	}
 
-	snprintf(result, len, "%s, %s%s, %s clock, %s mode, p1 = %d, "
+	return z_snprintf(result, len, "%s, %s%s, %s clock, %s mode, p1 = %d, "
 			 "p2 = %d%s%s",
 			 enabled, dvomode, vgamode, clock, mode, p1, p2,
 			 fpextra, sdvoextra);
@@ -556,7 +589,7 @@ DEBUGSTRING(i830_debug_dpll_test)
 	const char *dpllbinput = val & DPLLB_INPUT_BUFFER_ENABLE ?
 	    "" : ", DPLLB input buffer disabled";
 
-	snprintf(result, len, "%s%s%s%s%s%s",
+	return z_snprintf(result, len, "%s%s%s%s%s%s",
 			 dpllandiv, dpllamdiv, dpllainput,
 			 dpllbndiv, dpllbmdiv, dpllbinput);
 }
@@ -572,10 +605,10 @@ DEBUGSTRING(i830_debug_adpa)
 		disp_pipe = val & (1<<29) ? 'B' : 'A';
 
 	if (HAS_PCH_SPLIT(devid))
-		snprintf(result, len, "%s, transcoder %c, %chsync, %cvsync",
+		return z_snprintf(result, len, "%s, transcoder %c, %chsync, %cvsync",
 				 enable, disp_pipe, hsync, vsync);
 	else
-		snprintf(result, len, "%s, pipe %c, %chsync, %cvsync",
+		return z_snprintf(result, len, "%s, pipe %c, %chsync, %cvsync",
 				 enable, disp_pipe, hsync, vsync);
 }
 
@@ -598,7 +631,7 @@ DEBUGSTRING(i830_debug_lvds)
 	if (HAS_CPT)
 		disp_pipe = val & (1<<29) ? 'B' : 'A';
 
-	snprintf(result, len, "%s, pipe %c, %d bit, %s",
+	return z_snprintf(result, len, "%s, pipe %c, %d bit, %s",
 			 enable, disp_pipe, depth, channels);
 }
 
@@ -625,7 +658,7 @@ DEBUGSTRING(i830_debug_dvo)
 		break;
 	}
 
-	snprintf(result, len, "%s, pipe %c, %s, %chsync, %cvsync",
+	return z_snprintf(result, len, "%s, pipe %c, %s, %chsync, %cvsync",
 			 enable, disp_pipe, stall, hsync, vsync);
 }
 
@@ -646,7 +679,7 @@ DEBUGSTRING(i830_debug_sdvo)
 		sdvoextra[0] = '\0';
 	}
 
-	snprintf(result, len, "%s, pipe %c, stall %s, %sdetected%s%s",
+	return z_snprintf(result, len, "%s, pipe %c, stall %s, %sdetected%s%s",
 			 enable, disp_pipe, stall, detected, sdvoextra, gang);
 }
 
@@ -685,7 +718,7 @@ DEBUGSTRING(i830_debug_dspclk_gate_d)
 	const char *OVUUNIT = val & OVUUNIT_CLOCK_GATE_DISABLE ? " OVUUNIT" : "";
 	const char *OVLUNIT = val & OVLUNIT_CLOCK_GATE_DISABLE ? " OVLUNIT" : "";
 
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "clock gates disabled:%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
 		 DPUNIT_B, VSUNIT, VRHUNIT, VRDUNIT, AUDUNIT, DPUNIT_A, DPCUNIT,
 		 TVRUNIT, TVCUNIT, TVFUNIT, TVEUNIT, DVSUNIT, DSSUNIT, DDBUNIT,
@@ -702,16 +735,16 @@ DEBUGSTRING(i810_debug_915_fence)
 	int size = (1024 * 1024) << ((val & 0x700) >> 8);
 
 	if (IS_GEN4(devid) || (IS_915(devid) && reg >= FENCE_NEW))
-		return;
+		return 0;
 
 	if (format == 'X')
 		pitch *= 4;
 	if (val & 1) {
-		snprintf(result, len, "enabled, %c tiled, %4d pitch, 0x%08x - 0x%08x (%dkb)",
+		return z_snprintf(result, len, "enabled, %c tiled, %4d pitch, 0x%08x - 0x%08x (%dkb)",
 			 format, pitch, offset, offset + size,
 			 size / 1024);
 	} else {
-		snprintf(result, len, "disabled");
+		return z_snprintf(result, len, "disabled");
 	}
 }
 
@@ -723,9 +756,9 @@ DEBUGSTRING(i810_debug_965_fence_start)
 	unsigned int offset = val & 0xfffff000;
 
 	if (!IS_GEN4(devid))
-		return;
+		return 0;
 
-	snprintf(result, len, "%s, %c tile walk, %4d pitch, 0x%08x start",
+	return z_snprintf(result, len, "%s, %c tile walk, %4d pitch, 0x%08x start",
 		 enable, format, pitch, offset);
 }
 
@@ -734,9 +767,9 @@ DEBUGSTRING(i810_debug_965_fence_end)
 	unsigned int end = val & 0xfffff000;
 
 	if (!IS_GEN4(devid))
-		return;
+		return 0;
 
-	snprintf(result, len, "                                   0x%08x end", end);
+	return z_snprintf(result, len, "                                   0x%08x end", end);
 }
 
 #define DEFINEREG(reg) \
@@ -1017,19 +1050,19 @@ static const struct reg_debug intel_debug_regs[] = {
 
 DEBUGSTRING(ironlake_debug_rr_hw_ctl)
 {
-	snprintf(result, len, "low %d, high %d", val & RR_HW_LOW_POWER_FRAMES_MASK,
+	return z_snprintf(result, len, "low %d, high %d", val & RR_HW_LOW_POWER_FRAMES_MASK,
 		 (val & RR_HW_HIGH_POWER_FRAMES_MASK) >> 8);
 }
 
 DEBUGSTRING(ironlake_debug_m_tu)
 {
-	snprintf(result, len, "TU %d, val 0x%x %d", (val >> 25) + 1, val & 0xffffff,
+	return z_snprintf(result, len, "TU %d, val 0x%x %d", (val >> 25) + 1, val & 0xffffff,
 		 val & 0xffffff);
 }
 
 DEBUGSTRING(ironlake_debug_n)
 {
-	snprintf(result, len, "val 0x%x %d", val & 0xffffff, val & 0xffffff);
+	return z_snprintf(result, len, "val 0x%x %d", val & 0xffffff, val & 0xffffff);
 }
 
 DEBUGSTRING(ironlake_debug_fdi_tx_ctl)
@@ -1126,7 +1159,7 @@ DEBUGSTRING(ironlake_debug_fdi_tx_ctl)
 		break;
 	}
 
-	snprintf(result, len, "%s, train pattern %s, voltage swing %s,"
+	return z_snprintf(result, len, "%s, train pattern %s, voltage swing %s,"
 		 "pre-emphasis %s, port width %s, enhanced framing %s, FDI PLL %s, scrambing %s, master mode %s",
 		 val & FDI_TX_ENABLE ? "enable" : "disable",
 		 train, voltage, pre_emphasis, portw,
@@ -1203,7 +1236,7 @@ DEBUGSTRING(ironlake_debug_fdi_rx_ctl)
 		break;
 	}
 
-	snprintf(result, len, "%s, train pattern %s, port width %s, %s,"
+	return z_snprintf(result, len, "%s, train pattern %s, port width %s, %s,"
 		 "link_reverse_strap_overwrite %s, dmi_link_reverse %s, FDI PLL %s,"
 		 "FS ecc %s, FE ecc %s, FS err report %s, FE err report %s,"
 		 "scrambing %s, enhanced framing %s, %s",
@@ -1223,7 +1256,7 @@ DEBUGSTRING(ironlake_debug_fdi_rx_ctl)
 
 DEBUGSTRING(ironlake_debug_dspstride)
 {
-	snprintf(result, len, "%d", val >> 6);
+	return z_snprintf(result, len, "%d", val >> 6);
 }
 
 DEBUGSTRING(ironlake_debug_pch_dpll)
@@ -1272,7 +1305,7 @@ DEBUGSTRING(ironlake_debug_pch_dpll)
 
 	sdvo_mul = ((val & PLL_REF_SDVO_HDMI_MULTIPLIER_MASK) >> 9) + 1;
 
-	snprintf(result, len, "%s, sdvo high speed %s, mode %s, p2 %s, "
+	return z_snprintf(result, len, "%s, sdvo high speed %s, mode %s, p2 %s, "
 		 "FPA0 P1 %d, FPA1 P1 %d, refclk %s, sdvo/hdmi mul %d",
 		 enable, highspeed, mode, p2, fpa0_p1, fpa1_p1, refclk,
 		 sdvo_mul);
@@ -1304,7 +1337,7 @@ DEBUGSTRING(ironlake_debug_dref_ctl)
 	default:
 		cpu_source = "reserved";
 	}
-	snprintf(result, len, "cpu source %s, ssc_source %s, nonspread_source %s, "
+	return z_snprintf(result, len, "cpu source %s, ssc_source %s, nonspread_source %s, "
 		 "superspread_source %s, ssc4_mode %s, ssc1 %s, ssc4 %s",
 		 cpu_source, ssc_source, nonspread_source,
 		 superspread_source, ssc4_mode, ssc1, ssc4);
@@ -1342,14 +1375,14 @@ DEBUGSTRING(ironlake_debug_rawclk_freq)
 		tp2 = "12.0us";
 		break;
 	}
-	snprintf(result, len, "FDL_TP1 timer %s, FDL_TP2 timer %s, freq %d",
+	return z_snprintf(result, len, "FDL_TP1 timer %s, FDL_TP2 timer %s, freq %d",
 		 tp1, tp2, val & RAWCLK_FREQ_MASK);
 
 }
 
 DEBUGSTRING(ironlake_debug_fdi_rx_misc)
 {
-	snprintf(result, len, "FDI Delay %d", val & ((1 << 13) - 1));
+	return z_snprintf(result, len, "FDI Delay %d", val & ((1 << 13) - 1));
 }
 
 DEBUGSTRING(ironlake_debug_transconf)
@@ -1375,7 +1408,7 @@ DEBUGSTRING(ironlake_debug_transconf)
 		interlace = "rsvd";
 	}
 
-	snprintf(result, len, "%s, %s, %s", enable, state, interlace);
+	return z_snprintf(result, len, "%s, %s, %s", enable, state, interlace);
 }
 
 DEBUGSTRING(ironlake_debug_panel_fitting)
@@ -1412,7 +1445,7 @@ DEBUGSTRING(ironlake_debug_panel_fitting)
 		break;
 	}
 
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "%s, auto_scale %s, auto_scale_cal %s, v_filter %s, vadapt %s, mode %s, filter_sel %s,"
 		 "chroma pre-filter %s, vert3tap %s, v_inter_invert %s",
 		 val & PF_ENABLE ? "enable" : "disable",
@@ -1429,21 +1462,21 @@ DEBUGSTRING(ironlake_debug_panel_fitting)
 
 DEBUGSTRING(ironlake_debug_panel_fitting_2)
 {
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "vscale %f",
 		 val / (float) (1<<15));
 }
 
 DEBUGSTRING(ironlake_debug_panel_fitting_3)
 {
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "vscale initial phase %f",
 		 val / (float) (1<<15));
 }
 
 DEBUGSTRING(ironlake_debug_panel_fitting_4)
 {
-	snprintf(result, len,
+	return z_snprintf(result, len,
 		 "hscale %f",
 		 val / (float) (1<<15));
 }
@@ -1455,7 +1488,7 @@ DEBUGSTRING(ironlake_debug_pf_win)
 	a = (val >> 16) & 0x1fff;
 	b = val & 0xfff;
 
-	snprintf(result, len, "%d, %d", a, b);
+	return z_snprintf(result, len, "%d, %d", a, b);
 }
 
 DEBUGSTRING(ironlake_debug_hdmi)
@@ -1513,7 +1546,7 @@ DEBUGSTRING(ironlake_debug_hdmi)
 	else
 		detect = "non-detected";
 
-	snprintf(result, len, "%s pipe %c %s %s %s audio %s %s %s %s",
+	return z_snprintf(result, len, "%s pipe %c %s %s %s audio %s %s %s %s",
 		 enable, disp_pipe + 'A', bpc, encoding, mode, audio, vsync, hsync, detect);
 }
 
@@ -1523,7 +1556,7 @@ DEBUGSTRING(snb_debug_dpll_sel)
 	const char *dplla = NULL, *dpllb = NULL;
 
 	if (!HAS_CPT)
-		return;
+		return 0;
 
 	if (val & TRANSA_DPLL_ENABLE) {
 		transa = "enable";
@@ -1543,7 +1576,7 @@ DEBUGSTRING(snb_debug_dpll_sel)
 	} else
 		transb = "disable";
 
-	snprintf(result, len, "TransA DPLL %s (DPLL %s), TransB DPLL %s (DPLL %s)",
+	return z_snprintf(result, len, "TransA DPLL %s (DPLL %s), TransB DPLL %s (DPLL %s)",
 		 transa, dplla, transb, dpllb);
 }
 
@@ -1552,7 +1585,7 @@ DEBUGSTRING(snb_debug_trans_dp_ctl)
 	const char *enable, *port = NULL, *bpc = NULL, *vsync, *hsync;
 
 	if (!HAS_CPT)
-		return;
+		return 0;
 
 	if (val & TRANS_DP_OUTPUT_ENABLE)
 		enable = "enable";
@@ -1599,13 +1632,13 @@ DEBUGSTRING(snb_debug_trans_dp_ctl)
 	else
 		hsync = "-hsync";
 
-	snprintf(result, len, "%s port %s %s %s %s",
+	return z_snprintf(result, len, "%s port %s %s %s %s",
 		 enable, port, bpc, vsync, hsync);
 }
 
 DEBUGSTRING(ilk_debug_pp_control)
 {
-	snprintf(result, len, "blacklight %s, %spower down on reset, panel %s",
+	return z_snprintf(result, len, "blacklight %s, %spower down on reset, panel %s",
 		 (val & (1 << 2)) ? "enabled" : "disabled",
 		 (val & (1 << 1)) ? "" : "do not ",
 		 (val & (1 << 0)) ? "on" : "off");
@@ -1642,7 +1675,7 @@ DEBUGSTRING(hsw_debug_port_clk_sel)
 		break;
 	}
 
-	snprintf(result, len, "%s", clock);
+	return z_snprintf(result, len, "%s", clock);
 }
 
 DEBUGSTRING(hsw_debug_pipe_clk_sel)
@@ -1670,7 +1703,7 @@ DEBUGSTRING(hsw_debug_pipe_clk_sel)
 		break;
 	}
 
-	snprintf(result, len, "%s", clock);
+	return z_snprintf(result, len, "%s", clock);
 }
 
 DEBUGSTRING(hsw_debug_ddi_buf_ctl)
@@ -1697,7 +1730,7 @@ DEBUGSTRING(hsw_debug_ddi_buf_ctl)
 
 	detected = (val & 1) ? "detected" : "not detected";
 
-	snprintf(result, len, "%s %s %s %s", enable, reversal, width, detected);
+	return z_snprintf(result, len, "%s %s %s %s", enable, reversal, width, detected);
 }
 
 DEBUGSTRING(hsw_debug_sfuse_strap)
@@ -1711,7 +1744,7 @@ DEBUGSTRING(hsw_debug_sfuse_strap)
 	portc = (val & (1<<1)) ? "yes" : "no";
 	portd = (val & (1<<0)) ? "yes" : "no";
 
-	snprintf(result, len, "display %s, crt %s, lane reversal %s, "
+	return z_snprintf(result, len, "display %s, crt %s, lane reversal %s, "
 		 "port b %s, port c %s, port d %s", display, crt, lane_reversal,
 		 portb, portc, portd);
 }
@@ -1820,7 +1853,7 @@ DEBUGSTRING(hsw_debug_pipe_ddi_func_ctl)
 		break;
 	}
 
-	snprintf(result, len, "%s, %s, %s, %s, %s, %s, %s, %s", enable,
+	return z_snprintf(result, len, "%s, %s, %s, %s, %s, %s, %s, %s", enable,
 		 port, mode, bpc, vsync, hsync, edp_input, width);
 }
 
@@ -1832,7 +1865,7 @@ DEBUGSTRING(hsw_debug_wm_pipe)
 	sprite = (val >> 8) & 0x7F;
 	cursor = val & 0x3F;
 
-	snprintf(result, len, "primary %d, sprite %d, pipe %d", primary,
+	return z_snprintf(result, len, "primary %d, sprite %d, pipe %d", primary,
 		 sprite, cursor);
 }
 
@@ -1847,7 +1880,7 @@ DEBUGSTRING(hsw_debug_lp_wm)
 	pri = (val >> 8) & 0x3FF;
 	cur = val & 0xFF;
 
-	snprintf(result, len, "%s, latency %d, fbc %d, pri %d, cur %d",
+	return z_snprintf(result, len, "%s, latency %d, fbc %d, pri %d, cur %d",
 		 enable, latency, fbc, pri, cur);
 }
 
@@ -1860,7 +1893,7 @@ DEBUGSTRING(hsw_debug_sinterrupt)
 	portb = (val >> 21) & 1;
 	crt = (val >> 19) & 1;
 
-	snprintf(result, len, "port d:%d, port c:%d, port b:%d, crt:%d",
+	return z_snprintf(result, len, "port d:%d, port c:%d, port b:%d, crt:%d",
 		 portd, portc, portb, crt);
 }
 
@@ -1894,12 +1927,12 @@ DEBUGSTRING(ilk_debug_blc_pwm_cpu_ctl2)
 	}
 
 	if (IS_GEN5(devid) || IS_GEN6(devid) || IS_IVYBRIDGE(devid)) {
-		snprintf(result, len, "enable %d, pipe %s", enable, pipe);
+		return z_snprintf(result, len, "enable %d, pipe %s", enable, pipe);
 	} else {
 		blinking = (val >> 28) & 1;
 		granularity = ((val >> 27) & 1) ? 8 : 128;
 
-		snprintf(result, len, "enable %d, pipe %s, blinking %d, "
+		return z_snprintf(result, len, "enable %d, pipe %s, blinking %d, "
 			 "granularity %d", enable, pipe, blinking,
 			 granularity);
 	}
@@ -1912,11 +1945,11 @@ DEBUGSTRING(ilk_debug_blc_pwm_cpu_ctl)
 	cycle = (val & 0xFFFF);
 
 	if (IS_GEN5(devid) || IS_GEN6(devid) || IS_IVYBRIDGE(devid)) {
-		snprintf(result, len, "cycle %d", cycle);
+		return z_snprintf(result, len, "cycle %d", cycle);
 	} else {
 		freq = (val >> 16) & 0xFFFF;
 
-		snprintf(result, len, "cycle %d, freq %d", cycle, freq);
+		return z_snprintf(result, len, "cycle %d, freq %d", cycle, freq);
 	}
 }
 
@@ -1928,7 +1961,7 @@ DEBUGSTRING(ibx_debug_blc_pwm_ctl1)
 	override = (val >> 30) & 1;
 	inverted_polarity = (val >> 29) & 1;
 
-	snprintf(result, len, "enable %d, override %d, inverted polarity %d",
+	return z_snprintf(result, len, "enable %d, override %d, inverted polarity %d",
 		 enable, override, inverted_polarity);
 }
 
@@ -1939,7 +1972,7 @@ DEBUGSTRING(ibx_debug_blc_pwm_ctl2)
 	freq = (val >> 16) & 0xFFFF;
 	cycle = val & 0xFFFF;
 
-	snprintf(result, len, "freq %d, cycle %d", freq, cycle);
+	return z_snprintf(result, len, "freq %d, cycle %d", freq, cycle);
 }
 
 DEBUGSTRING(hsw_debug_blc_misc_ctl)
@@ -1948,7 +1981,7 @@ DEBUGSTRING(hsw_debug_blc_misc_ctl)
 
 	sel = (val & 1) ? "PWM1-CPU PWM2-PCH" : "PWM1-PCH PWM2-CPU";
 
-	snprintf(result, len, "%s", sel);
+	return z_snprintf(result, len, "%s", sel);
 }
 
 DEBUGSTRING(hsw_debug_util_pin_ctl)
@@ -1994,7 +2027,7 @@ DEBUGSTRING(hsw_debug_util_pin_ctl)
 	data = (val >> 23) & 1;
 	inverted_polarity = (val >> 22) & 1;
 
-	snprintf(result, len, "enable %d, transcoder %s, mode %s, data %d "
+	return z_snprintf(result, len, "enable %d, transcoder %s, mode %s, data %d "
 		 "inverted polarity %d", enable, transcoder, mode, data,
 		 inverted_polarity);
 }
@@ -2530,7 +2563,7 @@ static const struct reg_debug i945gm_mi_regs[] = {
 
 DEBUGSTRING(gen6_rp_control)
 {
-	snprintf(result, len, "%s",
+	return z_snprintf(result, len, "%s",
 		 (val & (1 << 7)) ? "enabled" : "disabled");
 }
 
@@ -2631,13 +2664,15 @@ int intel_reg_spec_decode(char *buf, size_t bufsize, const struct reg *reg,
 			if (reg->addr != r->reg)
 				continue;
 
-			if (r->debug_output)
-				r->debug_output(tmp, sizeof(tmp), r->reg,
-						val, devid);
-			else if (devid)
+			if (r->debug_output) {
+				if (r->debug_output(tmp, sizeof(tmp), r->reg,
+						    val, devid) == 0)
+					continue;
+			} else if (devid) {
 				return 0;
-			else
+			} else {
 				continue;
+			}
 
 			if (devid) {
 				strncpy(buf, tmp, bufsize);