mmc: implement Driver Stage Register handling

Some eMMC and SD cards implement a DSR register that allows to tune
raise/fall times and drive strength of the CMD and DATA outputs.
The values to use depend on the card in use and the host.
It might be needed to reduce the drive strength to prevent voltage peaks
above the host's specification.

Implement a 'dsr' devicetree property that allows to specify the value
to set the DSR to. For non-dt setups the new members of mmc_host can be
set by board code.

This patch was initially authored by Sascha Hauer. It contains
improvements authored by Markus Niebel and Uwe Kleine-König.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Markus Niebel <Markus.Niebel@tq-group.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

8 files changed, 52 insertions, 1 deletions

diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
index 431716e37a39..b52628b18a53 100644
--- a/Documentation/devicetree/bindings/mmc/mmc.txt
+++ b/Documentation/devicetree/bindings/mmc/mmc.txt
@@ -40,6 +40,8 @@ Optional properties:
 - mmc-hs200-1_2v: eMMC HS200 mode(1.2V I/O) is supported
 - mmc-hs400-1_8v: eMMC HS400 mode(1.8V I/O) is supported
 - mmc-hs400-1_2v: eMMC HS400 mode(1.2V I/O) is supported
+- dsr: Value the card's (optional) Driver Stage Register (DSR) should be
+  programmed with. Valid range: [0 .. 0xffff].
 
 *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
 polarity properties, we have to fix the meaning of the "normal" and "inverted"
diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index 95cceae96944..d572b2beb65a 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -452,6 +452,14 @@ int mmc_of_parse(struct mmc_host *host)
 	if (of_find_property(np, "mmc-hs400-1_2v", &len))
 		host->caps2 |= MMC_CAP2_HS400_1_2V | MMC_CAP2_HS200_1_2V_SDR;
 
+	host->dsr_req = !of_property_read_u32(np, "dsr", &host->dsr);
+	if (host->dsr_req && (host->dsr & ~0xffff)) {
+		dev_err(host->parent,
+			"device tree specified broken value for DSR: 0x%x, ignoring\n",
+			host->dsr);
+		host->dsr_req = 0;
+	}
+
 	return 0;
 
 out:
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 1eda8dd8c867..31c43165f8bc 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -162,6 +162,7 @@ static int mmc_decode_csd(struct mmc_card *card)
 	csd->read_partial = UNSTUFF_BITS(resp, 79, 1);
 	csd->write_misalign = UNSTUFF_BITS(resp, 78, 1);
 	csd->read_misalign = UNSTUFF_BITS(resp, 77, 1);
+	csd->dsr_imp = UNSTUFF_BITS(resp, 76, 1);
 	csd->r2w_factor = UNSTUFF_BITS(resp, 26, 3);
 	csd->write_blkbits = UNSTUFF_BITS(resp, 22, 4);
 	csd->write_partial = UNSTUFF_BITS(resp, 21, 1);
@@ -1272,6 +1273,13 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 	}
 
 	/*
+	 * handling only for cards supporting DSR and hosts requesting
+	 * DSR configuration
+	 */
+	if (card->csd.dsr_imp && host->dsr_req)
+		mmc_set_dsr(host);
+
+	/*
 	 * Select card, as all following commands rely on that.
 	 */
 	if (!mmc_host_is_spi(host)) {
diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index f51b5ba3bbea..ba0275e90617 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -93,6 +93,26 @@ int mmc_deselect_cards(struct mmc_host *host)
 	return _mmc_select_card(host, NULL);
 }
 
+/*
+ * Write the value specified in the device tree or board code into the optional
+ * 16 bit Driver Stage Register. This can be used to tune raise/fall times and
+ * drive strength of the DAT and CMD outputs. The actual meaning of a given
+ * value is hardware dependant.
+ * The presence of the DSR register can be determined from the CSD register,
+ * bit 76.
+ */
+int mmc_set_dsr(struct mmc_host *host)
+{
+	struct mmc_command cmd = {0};
+
+	cmd.opcode = MMC_SET_DSR;
+
+	cmd.arg = (host->dsr << 16) | 0xffff;
+	cmd.flags = MMC_RSP_NONE | MMC_CMD_AC;
+
+	return mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);
+}
+
 int mmc_go_idle(struct mmc_host *host)
 {
 	int err;
diff --git a/drivers/mmc/core/mmc_ops.h b/drivers/mmc/core/mmc_ops.h
index 80ae9f4e0293..390dac665b2a 100644
--- a/drivers/mmc/core/mmc_ops.h
+++ b/drivers/mmc/core/mmc_ops.h
@@ -14,6 +14,7 @@
 
 int mmc_select_card(struct mmc_card *card);
 int mmc_deselect_cards(struct mmc_host *host);
+int mmc_set_dsr(struct mmc_host *host);
 int mmc_go_idle(struct mmc_host *host);
 int mmc_send_op_cond(struct mmc_host *host, u32 ocr, u32 *rocr);
 int mmc_all_send_cid(struct mmc_host *host, u32 *cid);
diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
index 0c44510bf717..25913889cbaa 100644
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -127,6 +127,7 @@ static int mmc_decode_csd(struct mmc_card *card)
 		csd->read_partial = UNSTUFF_BITS(resp, 79, 1);
 		csd->write_misalign = UNSTUFF_BITS(resp, 78, 1);
 		csd->read_misalign = UNSTUFF_BITS(resp, 77, 1);
+		csd->dsr_imp = UNSTUFF_BITS(resp, 76, 1);
 		csd->r2w_factor = UNSTUFF_BITS(resp, 26, 3);
 		csd->write_blkbits = UNSTUFF_BITS(resp, 22, 4);
 		csd->write_partial = UNSTUFF_BITS(resp, 21, 1);
@@ -954,6 +955,13 @@ static int mmc_sd_init_card(struct mmc_host *host, u32 ocr,
 	}
 
 	/*
+	 * handling only for cards supporting DSR and hosts requesting
+	 * DSR configuration
+	 */
+	if (card->csd.dsr_imp && host->dsr_req)
+		mmc_set_dsr(host);
+
+	/*
 	 * Select card, as all following commands rely on that.
 	 */
 	if (!mmc_host_is_spi(host)) {
diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
index bde5147a4221..0ea795f5feb9 100644
--- a/include/linux/mmc/card.h
+++ b/include/linux/mmc/card.h
@@ -42,7 +42,8 @@ struct mmc_csd {
 	unsigned int		read_partial:1,
 				read_misalign:1,
 				write_partial:1,
-				write_misalign:1;
+				write_misalign:1,
+				dsr_imp:1;
 };
 
 struct mmc_ext_csd {
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 7960424d0bc0..4cbf61476999 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -365,6 +365,9 @@ struct mmc_host {
 
 	unsigned int		slotno;	/* used for sdio acpi binding */
 
+	int			dsr_req;	/* DSR value is valid */
+	u32			dsr;	/* optional driver stage (DSR) value */
+
 	unsigned long		private[0] ____cacheline_aligned;
 };