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

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On 13 August 2014 17:44, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: Markus Niebel <Markus.Niebel@xxxxxxxxxxxx>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> ---
> 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
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