Re: [PATCH v3] mmc: implement Driver Stage Register handling

Ulf Hansson
2014-08-14T09:26:29Z

On 13 August 2014 17:44, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> wrote:
> From: Sascha Hauer <s.hauer@pengutronix.de>
>
> Some (e)MMC 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>
> ---
> Hello,
>
> earlier incarnations of this patch can be found at
>
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/272983.html
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/259281.html
>
> I need this functionallity on a machine where the default driver strength of
> the eMMC chip is too big for the SoC. It seems to work without adapting the
> drive strength, but the vendor reports that the DSR should be set to a certain
> value to prevent poor signal integrity and increased wearout.
>
> Best regards
> Uwe
>
> Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
> drivers/mmc/core/host.c | 8 ++++++++
> drivers/mmc/core/mmc.c | 8 ++++++++
> drivers/mmc/core/mmc_ops.c | 21 +++++++++++++++++++++
> drivers/mmc/core/mmc_ops.h | 1 +
> drivers/mmc/core/sd.c | 8 ++++++++
> include/linux/mmc/card.h | 3 ++-
> include/linux/mmc/host.h | 3 +++
> 8 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index 3c18001dfd5d..05bac770b4d0 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.

Let's clarify that this is a 16 bit value.

>
> *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..52e83f389428 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;
>
> + if (of_find_property(np, "dsr", &len)) {
> + u32 tmp;
> +
> + of_property_read_u32(np, "dsr", &tmp);
> + host->dsr_req = 1;
> + host->dsr = (u16)tmp;
> + }
> +

Let's simplify the above with just:
of_property_read_u16(np, "dsr", &host->dsr);

> return 0;
>
> out:
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 793c6f7ddb04..fdc1ac1360c4 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);
> @@ -1273,6 +1274,13 @@ 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)

We don't need host->dsr_req. Instead just check host->dsr.

> + 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..37ed493d8030 100644
> --- a/drivers/mmc/core/mmc_ops.c
> +++ b/drivers/mmc/core/mmc_ops.c
> @@ -93,6 +93,27 @@ 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)
> +{
> + int err;
> + struct mmc_command cmd = {0};
> +
> + cmd.opcode = MMC_SET_DSR;
> +
> + cmd.arg = ((u32)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)

Check host->dsr instead.

> + 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 d424b9de3aff..680a7f0188bb 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..9e9ad7b31bb9 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -319,6 +319,7 @@ struct mmc_host {
> #ifdef CONFIG_MMC_DEBUG
> unsigned int removed:1; /* host is being removed */
> #endif
> + unsigned int dsr_req:1; /* DSR is requested for Host */

Remove dsr_req.

>
> int rescan_disable; /* disable card detection */
> int rescan_entered; /* used with nonremovable devices */
> @@ -365,6 +366,8 @@ struct mmc_host {
>
> unsigned int slotno; /* used for sdio acpi binding */
>
> + u16 dsr; /* optional driver stage (dsr) value */
> +
> unsigned long private[0] ____cacheline_aligned;
> };
>
> --
> 2.0.1
>

Kind regards
Uffe