Commit 3d705d14 authored by Sascha Hauer's avatar Sascha Hauer Committed by Ulf Hansson
Browse files

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: default avatarSascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: default avatarMarkus Niebel <Markus.Niebel@tq-group.com>
Signed-off-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
parent b3153765

Documentation/devicetree/bindings/mmc/mmc.txt

+2 −0
Original line number Diff line number Diff line
@@ -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"

drivers/mmc/core/host.c

+8 −0
Original line number Diff line number Diff line
@@ -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:

drivers/mmc/core/mmc.c

+8 −0
Original line number Diff line number Diff line
@@ -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);
@@ -1271,6 +1272,13 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr, 
			goto free_card;

	}



	/*

	 * 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.

	 */

drivers/mmc/core/mmc_ops.c

+20 −0
Original line number Diff line number Diff line
@@ -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;

drivers/mmc/core/mmc_ops.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

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