[PATCH] mmc: implement driver stage register handling

[Sascha Hauer]

The eMMC and the SD-Card specifications describe the optional SET_DSR command.
During measurements at our lab we found that some cards implementing this feature
having really strong driver strengts per default. This can lead to voltage peaks
above the specification of the host on signal edges for data sent from a card to
the host.

Since availability of a given card type may be shorter than the time a certain
hardware will be produced it is useful to have support for this command (Alternative
would be changing termination resistors and adapting the driver strength of the
host to the used card.)

As the value of the dsr register is board specific this adds a 'dsr' devicetree
property which is handled in mmc_of_parse.

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 Documentation/devicetree/bindings/mmc/mmc.txt |  3 +++
 drivers/mmc/core/host.c                       |  3 +++
 drivers/mmc/core/mmc.c                        |  4 ++++
 drivers/mmc/core/mmc_ops.c                    | 17 +++++++++++++++++
 drivers/mmc/core/mmc_ops.h                    |  1 +
 include/linux/mmc/card.h                      |  3 ++-
 include/linux/mmc/host.h                      |  2 ++
 7 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
index 9dce540..737203e 100644
--- a/Documentation/devicetree/bindings/mmc/mmc.txt
+++ b/Documentation/devicetree/bindings/mmc/mmc.txt
@@ -38,6 +38,9 @@ Optional properties:
 - mmc-highspeed-ddr-1_2v: eMMC high-speed DDR mode(1.2V I/O) is supported
 - mmc-hs200-1_8v: eMMC HS200 mode(1.8V I/O) is supported
 - mmc-hs200-1_2v: eMMC HS200 mode(1.2V I/O) is supported
+- dsr: Content of the optional driver stage register (DSR) as described
+  in JEDEC Standard No. 84-A44, 12.4: Programmable card output driver. Not
+  all MMC cards implement this register and the actual value is card specific.
 
 *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 fdea825..eea272e 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -447,6 +447,7 @@ int mmc_of_parse(struct mmc_host *host)
 		host->caps2 |= MMC_CAP2_HS200_1_8V_SDR;
 	if (of_find_property(np, "mmc-hs200-1_2v", &len))
 		host->caps2 |= MMC_CAP2_HS200_1_2V_SDR;
+	of_property_read_u32(np, "dsr", &host->dsr);
 
 	return 0;
 
@@ -515,6 +516,8 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	host->max_blk_size = 512;
 	host->max_blk_count = PAGE_CACHE_SIZE / 512;
 
+	host->dsr = 0xffffffff;
+
 	return host;
 
 free:
diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 1ab5f3a..0ab1c44 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);
@@ -970,6 +971,9 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 			goto free_card;
 	}
 
+	if (card->csd.dsr_imp && (host->dsr & 0xffff) == host->dsr)
+		mmc_set_dsr(host);
+
 	/*
 	 * Select card, as all following commands rely on that.
 	 */
diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index f51b5ba..f8af72a 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -93,6 +93,23 @@ int mmc_deselect_cards(struct mmc_host *host)
 	return _mmc_select_card(host, NULL);
 }
 
+int mmc_set_dsr(struct mmc_host *host)
+{
+	int err;
+	struct mmc_command cmd = {0};
+
+	cmd.opcode = MMC_SET_DSR;
+
+	cmd.arg = (host->dsr << 16) | 0xffff;
+	cmd.flags = MMC_RSP_NONE | MMC_CMD_AC;
+
+	err = mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);
+	if (err)
+		return err;
+
+	return 0;
+}
+
 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 80ae9f4..390dac6 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/include/linux/mmc/card.h b/include/linux/mmc/card.h
index b730272..ced116f 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 cb61ea4..d8d9d68 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -358,6 +358,8 @@ struct mmc_host {
 
 	unsigned int		slotno;	/* used for sdio acpi binding */
 
+	u32			dsr;	/* optional driver stage register (dsr) value */
+
 	unsigned long		private[0] ____cacheline_aligned;
 };
 
-- 
2.0.0.rc0