tools: Add a simple tool to read/write/decode dpcd registers

This tool serves as a wrapper around the constructs provided by the
drm_dpcd_aux_dev kernel module by working on the /dev/drm_dp_aux[n]
devices created by the kernel module.
It supports reading and writing dpcd registers on the connected aux
channels.
In the follow-up patch, support for decoding these registers will be
added to facilate debugging panel related issues.

v2: (Fixes by Rodrigo but no functional changes yet):
    - Indentations, Typo, Missed spaces
    - Removing mentioning to decode and spec that is not implemented yet.
    - Add Makefile.sources back
    - Missed s/printf/igt_warn

v3:
    - Address DK's review comments from v2 above.
    - Squash Rodrigo's file handling unification patch.
    - Make count, offset and device id optional.

v4:
    - Better error handling and refactoring.

Suggested-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>

3 files changed, 282 insertions, 0 deletions

diff --git a/tools/Makefile.sources b/tools/Makefile.sources
index abd23a0f..50706f41 100644
--- a/tools/Makefile.sources
+++ b/tools/Makefile.sources
@@ -7,6 +7,7 @@ noinst_PROGRAMS =		\
 
 tools_prog_lists =		\
 	igt_stats		\
+	dpcd_reg		\
 	intel_audio_dump	\
 	intel_reg		\
 	intel_backlight		\
diff --git a/tools/dpcd_reg.c b/tools/dpcd_reg.c
new file mode 100644
index 00000000..d577aa55
--- /dev/null
+++ b/tools/dpcd_reg.c
@@ -0,0 +1,280 @@
+/*
+ * Copyright © 2018 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * DPCD register read/write tool
+ * This tool wraps around DRM_DP_AUX_DEV module to provide DPCD register read
+ * and write, so CONFIG_DRM_DP_AUX_DEV needs to be set.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <limits.h>
+#include <stdbool.h>
+
+#define MAX_DP_OFFSET	0xfffff
+#define DRM_AUX_MINORS	256
+
+const char aux_dev[] = "/dev/drm_dp_aux";
+
+struct dpcd_data {
+	int devid;
+	int file_op;
+	uint32_t offset;
+	enum command {
+		INVALID = -1,
+		READ = 2,
+		WRITE,
+	} cmd;
+	size_t count;
+	uint8_t val;
+};
+
+static void print_usage(void)
+{
+	printf("Usage: dpcd_reg [OPTION ...] COMMAND\n\n");
+	printf("COMMAND is one of:\n");
+	printf("  read:		Read [count] bytes dpcd reg at an offset\n");
+	printf("  write:	Write a dpcd reg at an offset\n\n");
+	printf("Options for the above COMMANDS are\n");
+	printf(" --device=DEVID		Aux device id, as listed in /dev/drm_dp_aux_dev[n]. Defaults to 0. Upper limit - 256\n");
+	printf(" --offset=REG_ADDR	DPCD register offset in hex. Defaults to 0x0. Upper limit - 0xfffff\n");
+	printf(" --count=BYTES		For reads, specify number of bytes to be read from the offset. Defaults to 1\n");
+	printf(" --value		For writes, specify a hex value to be written. Upper limit - 0xff\n\n");
+
+	printf(" --help: print the usage\n");
+}
+
+static inline bool strtol_err_util(char *endptr, long *val)
+{
+	if (*endptr != '\0' || *val < 0 ||
+	    (*val == LONG_MAX && errno == ERANGE))
+		return true;
+
+	return false;
+}
+
+static int parse_opts(struct dpcd_data *dpcd, int argc, char **argv)
+{
+	int ret, vflag = 0;
+	long temp;
+	char *endptr;
+
+	struct option longopts[] = {
+		{ "count",	required_argument,	NULL,		'c' },
+		{ "device",	required_argument,	NULL,		'd' },
+		{ "help",	no_argument,		NULL,		'h' },
+		{ "offset",	required_argument,	NULL,		'o' },
+		{ "value",	required_argument,	NULL,		'v' },
+		{ 0 }
+	};
+
+	while ((ret = getopt_long(argc, argv, "-:c:d:ho:v:", longopts, NULL)) != -1) {
+		switch (ret) {
+		case 'c':
+			temp = strtol(optarg, &endptr, 10);
+			if (strtol_err_util(endptr, &temp)) {
+				fprintf(stderr,
+					"--count argument is invalid/negative/out-of-range\n");
+				print_usage();
+				return EXIT_FAILURE;
+			}
+			dpcd->count = temp;
+			break;
+		case 'd':
+			temp = strtol(optarg, &endptr, 10);
+			if (strtol_err_util(endptr, &temp) ||
+					    temp > DRM_AUX_MINORS) {
+				fprintf(stderr,
+					"--device argument is invalid/negative/out-of-range\n");
+				print_usage();
+				return ERANGE;
+			}
+			dpcd->devid = temp;
+			break;
+		case 'h':
+			printf("DPCD register read and write tool\n\n");
+			printf("This tool requires CONFIG_DRM_DP_AUX_CHARDEV\n"
+				"to be set in the kernel config.\n\n");
+			print_usage();
+			exit(EXIT_SUCCESS);
+		case 'o':
+			temp = strtol(optarg, &endptr, 16);
+			if (strtol_err_util(endptr, &temp) ||
+					    temp > MAX_DP_OFFSET) {
+				fprintf(stderr,
+					"--offset argument is invalid/negative/out-of-range\n");
+				print_usage();
+				return ERANGE;
+			}
+			dpcd->offset = temp;
+			break;
+		case 'v':
+			vflag = 'v';
+			temp = strtol(optarg, &endptr, 16);
+			if (strtol_err_util(endptr, &temp) || temp > 0xff) {
+				fprintf(stderr,
+					"--value argument is invalid/negative/out-of-range\n");
+				print_usage();
+				return ERANGE;
+			}
+			dpcd->val = temp;
+			break;
+		/* Command parsing */
+		case 1:
+			if (strcmp(optarg, "read") == 0) {
+				temp = READ;
+			} else if (strcmp(optarg, "write") == 0) {
+				temp = WRITE;
+				dpcd->file_op = O_WRONLY;
+			} else {
+				fprintf(stderr, "Unrecognized command\n");
+				print_usage();
+				return EXIT_FAILURE;
+			}
+			dpcd->cmd = temp;
+			break;
+		case ':':
+			fprintf(stderr, "Option -%c requires an argument\n",
+				 optopt);
+			print_usage();
+			return EXIT_FAILURE;
+		default:
+			fprintf(stderr, "Invalid option\n");
+			print_usage();
+			return EXIT_FAILURE;
+		}
+	}
+
+	if ((dpcd->count + dpcd->offset) > (MAX_DP_OFFSET + 1)) {
+		fprintf(stderr, "Out of bounds. Count + Offset <= 0x100000\n");
+		return ERANGE;
+	}
+
+	if ((dpcd->cmd == WRITE) && (vflag != 'v')) {
+		fprintf(stderr, "Write value is missing\n");
+		print_usage();
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+static int dpcd_read(int fd, uint32_t offset, size_t count)
+{
+	int ret = EXIT_SUCCESS, pret, i;
+	uint8_t *buf = calloc(count, sizeof(uint8_t));
+
+	if (!buf) {
+		fprintf(stderr, "Can't allocate read buffer\n");
+		return ENOMEM;
+	}
+
+	pret = pread(fd, buf, count, offset);
+	if (pret < 0) {
+		fprintf(stderr, "Failed to read - %s\n", strerror(errno));
+		ret = errno;
+		goto out;
+	}
+
+	if (pret < count) {
+		fprintf(stderr,
+			"Read %u byte(s), expected %zu bytes, starting at offset %x\n\n", pret, count, offset);
+		ret = EXIT_FAILURE;
+	}
+
+	printf("0x%02x: ", offset);
+	for (i = 0; i < pret; i++)
+		printf(" %02x", *(buf + i));
+	printf("\n");
+
+out:
+	free(buf);
+	return ret;
+}
+
+static int dpcd_write(int fd, uint32_t offset, uint8_t val)
+{
+	int ret = EXIT_SUCCESS, pret;
+
+	pret = pwrite(fd, (const void *)&val, sizeof(uint8_t), offset);
+	if (pret < 0) {
+		fprintf(stderr, "Failed to write - %s\n", strerror(errno));
+		ret = errno;
+	} else if (pret == 0) {
+		fprintf(stderr, "Zero bytes were written\n");
+		ret = EXIT_FAILURE;
+	}
+
+	return ret;
+}
+
+int main(int argc, char **argv)
+{
+	char dev_name[20];
+	int ret, fd;
+
+	struct dpcd_data dpcd = {
+		.devid = 0,
+		.file_op = O_RDONLY,
+		.offset = 0x0,
+		.cmd = INVALID,
+		.count = 1,
+	};
+
+	ret = parse_opts(&dpcd, argc, argv);
+	if (ret != EXIT_SUCCESS)
+		return ret;
+
+	snprintf(dev_name, strlen(aux_dev) + 4, "%s%d", aux_dev, dpcd.devid);
+
+	fd = open(dev_name, dpcd.file_op);
+	if (fd < 0) {
+		fprintf(stderr,
+			"Failed to open %s aux device - error: %s\n", dev_name,
+			strerror(errno));
+		return errno;
+	}
+
+	switch (dpcd.cmd) {
+	case READ:
+		ret = dpcd_read(fd, dpcd.offset, dpcd.count);
+		break;
+	case WRITE:
+		ret = dpcd_write(fd, dpcd.offset, dpcd.val);
+		break;
+	default:
+		fprintf(stderr, "Please specify a command: read/write.\n");
+		print_usage();
+		ret = EXIT_FAILURE;
+		break;
+	}
+
+	close(fd);
+
+	return ret;
+}
diff --git a/tools/meson.build b/tools/meson.build
index e4517d66..79f36aa9 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -36,6 +36,7 @@ tools_progs = [
 	'intel_watermark',
 	'intel_gem_info',
 	'intel_gvtg_test',
+	'dpcd_reg',
 ]
 tool_deps = igt_deps