Re: [PATCH v2 3/6] mmc: core: implement enhanced strobe support

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On 29 April 2016 at 04:47, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
> Controllers use data strobe line to latch data from devices
> under hs400 mode, but not for cmd line. So since emmc 5.1, JEDEC
> introduces enhanced strobe mode for latching cmd response from
> emmc devices to host controllers. This new feature is optional,
> so it depends both on device's cap and host's cap to decide
> whether to use it or not.
>
> Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> ---
>
> Changes in v2: None
>
>  drivers/mmc/core/bus.c   |  3 +-
>  drivers/mmc/core/mmc.c   | 77 ++++++++++++++++++++++++++++++++++++++++++++----
>  include/linux/mmc/card.h |  1 +
>  include/linux/mmc/host.h | 12 ++++++++
>  include/linux/mmc/mmc.h  |  3 ++
>  5 files changed, 89 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mmc/core/bus.c b/drivers/mmc/core/bus.c
> index 4bc48f1..7e94b9d 100644
> --- a/drivers/mmc/core/bus.c
> +++ b/drivers/mmc/core/bus.c
> @@ -332,12 +332,13 @@ int mmc_add_card(struct mmc_card *card)
>                         mmc_card_ddr52(card) ? "DDR " : "",
>                         type);
>         } else {
> -               pr_info("%s: new %s%s%s%s%s card at address %04x\n",
> +               pr_info("%s: new %s%s%s%s%s%s card at address %04x\n",
>                         mmc_hostname(card->host),
>                         mmc_card_uhs(card) ? "ultra high speed " :
>                         (mmc_card_hs(card) ? "high speed " : ""),
>                         mmc_card_hs400(card) ? "HS400 " :
>                         (mmc_card_hs200(card) ? "HS200 " : ""),
> +                       mmc_card_hs400es(card) ? "Enhanced strobe" : "",

I am not sure this informations should be printed. It's still and
HS400 card, there is no performance impact, right?

>                         mmc_card_ddr52(card) ? "DDR " : "",
>                         uhs_bus_speed_mode, type, card->rca);
>         }
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 28b477d..f45ed10 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -235,6 +235,12 @@ static void mmc_select_card_type(struct mmc_card *card)
>                 avail_type |= EXT_CSD_CARD_TYPE_HS400_1_2V;
>         }
>
> +       if ((caps2 & MMC_CAP2_HS400_ENHANCED_STROBE) &&
> +           card->ext_csd.strobe_support &&
> +           ((card_type & EXT_CSD_CARD_TYPE_HS400_1_2V) ||
> +            (card_type & EXT_CSD_CARD_TYPE_HS400_1_8V)))
> +               avail_type |= EXT_CSD_CARD_TYPE_HS400ES;
> +
>         card->ext_csd.hs_max_dtr = hs_max_dtr;
>         card->ext_csd.hs200_max_dtr = hs200_max_dtr;
>         card->mmc_avail_type = avail_type;
> @@ -383,6 +389,7 @@ static int mmc_decode_ext_csd(struct mmc_card *card, u8 *ext_csd)
>                         mmc_card_set_blockaddr(card);
>         }
>
> +       card->ext_csd.strobe_support = ext_csd[EXT_CSD_STROBE_SUPPORT];
>         card->ext_csd.raw_card_type = ext_csd[EXT_CSD_CARD_TYPE];
>         mmc_select_card_type(card);
>
> @@ -1062,9 +1069,10 @@ static int mmc_select_hs400(struct mmc_card *card)
>         u8 val;
>
>         /*
> -        * HS400 mode requires 8-bit bus width
> +        * HS400(ES) mode requires 8-bit bus width
>          */
> -       if (!(card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400 &&
> +       if (!(((card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400) ||
> +               (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES)) &&
>               host->ios.bus_width == MMC_BUS_WIDTH_8))
>                 return 0;
>
> @@ -1097,9 +1105,26 @@ static int mmc_select_hs400(struct mmc_card *card)
>         }
>
>         /* Switch card to DDR */
> +       val = EXT_CSD_DDR_BUS_WIDTH_8;
> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
> +               val |= EXT_CSD_BUS_WIDTH_STROBE;
> +               /*
> +               * Make sure we are in non-enhanced strobe mode before we
> +               * actually enable it in ext_csd.
> +               */
> +               if (host->ops->prepare_enhanced_strobe)
> +                       err = host->ops->prepare_enhanced_strobe(host, false);

1) I suggest we rename the callback to "hs400_enhanced_strobe".

2) I think this might be is a bit late to deal with restoring enhanced
strobe to off. Perhaps we should do that in mmc_set_initial_state()
instead!?

> +
> +               if (err) {
> +                       pr_err("%s: unprepare_enhanced strobe failed, err:%d\n",

Maybe pr_dbg instead?

/s/unprepare_enhanced strobe/Disable hs400 es

> +                               mmc_hostname(host), err);
> +                       return err;
> +               }
> +       }
> +
>         err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>                          EXT_CSD_BUS_WIDTH,
> -                        EXT_CSD_DDR_BUS_WIDTH_8,
> +                        val,
>                          card->ext_csd.generic_cmd6_time);
>         if (err) {
>                 pr_err("%s: switch to bus width for hs400 failed, err:%d\n",
> @@ -1124,6 +1149,35 @@ static int mmc_select_hs400(struct mmc_card *card)
>         mmc_set_timing(host, MMC_TIMING_MMC_HS400);
>         mmc_set_bus_speed(card);
>
> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
> +               /* Controller enable enhanced strobe function */
> +               if (host->ops->prepare_enhanced_strobe)
> +                       err = host->ops->prepare_enhanced_strobe(host, true);
> +
> +               if (err) {
> +                       pr_err("%s: prepare enhanced strobe failed, err:%d\n",

Maybe pr_dbg/warn instead?

/s/prepare enhanced strobe/Enable hs400 es

> +                               mmc_hostname(host), err);
> +                       return err;
> +               }
> +
> +               /*
> +                * After switching to hs400 enhanced strobe mode, we expect to
> +                * verify whether it works or not. If controller can't handle
> +                * bus width test, compare ext_csd previously read in 1 bit mode
> +                * against ext_csd at new bus width
> +                */

Is this according to spec? If so, we should probably state that here.
If not, further explanation for *why* we do this is needed.

> +               if (!(host->caps & MMC_CAP_BUS_WIDTH_TEST))
> +                       err = mmc_compare_ext_csds(card, MMC_BUS_WIDTH_8);
> +               else
> +                       err = mmc_bus_test(card, MMC_BUS_WIDTH_8);
> +
> +               if (err) {
> +                       pr_warn("%s: switch to enhanced strobe failed\n",
> +                               mmc_hostname(host));
> +                       return err;
> +               }
> +       }
> +
>         if (!send_status) {
>                 err = mmc_switch_status(card);
>                 if (err)
> @@ -1297,7 +1351,8 @@ err:
>  }
>
>  /*
> - * Activate High Speed or HS200 mode if supported.
> + * Activate High Speed or HS200 mode if supported. For HS400
> + * with enhanced strobe mode, we should activate High Speed.
>   */
>  static int mmc_select_timing(struct mmc_card *card)
>  {
> @@ -1306,7 +1361,9 @@ static int mmc_select_timing(struct mmc_card *card)
>         if (!mmc_can_ext_csd(card))
>                 goto bus_speed;
>
> -       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200)
> +       if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES)
> +               err = mmc_select_hs(card);
> +       else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS200)
>                 err = mmc_select_hs200(card);
>         else if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS)
>                 err = mmc_select_hs(card);
> @@ -1578,7 +1635,15 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>         } else if (mmc_card_hs(card)) {
>                 /* Select the desired bus width optionally */
>                 err = mmc_select_bus_width(card);
> -               if (!IS_ERR_VALUE(err)) {
> +               if (IS_ERR_VALUE(err))
> +                       goto free_card;

This is going to change the behaviour, as earlier switching the bus
width was optional. See the comment a few lines above and the
implementation of mmc_select_bus_width().

> +
> +               if (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES) {
> +                       /* Directly from HS to HS400-ES */
> +                       err = mmc_select_hs400(card);
> +                       if (err)
> +                               goto free_card;
> +               } else {
>                         err = mmc_select_hs_ddr(card);
>                         if (err)
>                                 goto free_card;
> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
> index eb0151b..22defc2 100644
> --- a/include/linux/mmc/card.h
> +++ b/include/linux/mmc/card.h
> @@ -95,6 +95,7 @@ struct mmc_ext_csd {
>         u8                      raw_partition_support;  /* 160 */
>         u8                      raw_rpmb_size_mult;     /* 168 */
>         u8                      raw_erased_mem_count;   /* 181 */
> +       u8                      strobe_support;         /* 184 */
>         u8                      raw_ext_csd_structure;  /* 194 */
>         u8                      raw_card_type;          /* 196 */
>         u8                      raw_driver_strength;    /* 197 */
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 11e89d3..19de56c 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -19,6 +19,7 @@
>
>  #include <linux/mmc/core.h>
>  #include <linux/mmc/card.h>
> +#include <linux/mmc/mmc.h>
>  #include <linux/mmc/pm.h>
>
>  struct mmc_ios {
> @@ -143,6 +144,8 @@ struct mmc_host_ops {
>
>         /* Prepare HS400 target operating frequency depending host driver */
>         int     (*prepare_hs400_tuning)(struct mmc_host *host, struct mmc_ios *ios);
> +       /* Prepare enhanced strobe depending host driver */
> +       int     (*prepare_enhanced_strobe)(struct mmc_host *host, bool enable);
>         int     (*select_drive_strength)(struct mmc_card *card,
>                                          unsigned int max_dtr, int host_drv,
>                                          int card_drv, int *drv_type);
> @@ -518,6 +521,15 @@ static inline bool mmc_card_hs400(struct mmc_card *card)
>         return card->host->ios.timing == MMC_TIMING_MMC_HS400;
>  }
>
> +static inline bool mmc_card_hs400es(struct mmc_card *card)
> +{
> +       if (mmc_card_hs400(card) &&
> +           (card->mmc_avail_type & EXT_CSD_CARD_TYPE_HS400ES))
> +               return 1;
> +
> +       return 0;
> +}
> +
>  void mmc_retune_timer_stop(struct mmc_host *host);
>
>  static inline void mmc_retune_needed(struct mmc_host *host)
> diff --git a/include/linux/mmc/mmc.h b/include/linux/mmc/mmc.h
> index 15f2c4a..c376209 100644
> --- a/include/linux/mmc/mmc.h
> +++ b/include/linux/mmc/mmc.h
> @@ -297,6 +297,7 @@ struct _mmc_csd {
>  #define EXT_CSD_PART_CONFIG            179     /* R/W */
>  #define EXT_CSD_ERASED_MEM_CONT                181     /* RO */
>  #define EXT_CSD_BUS_WIDTH              183     /* R/W */
> +#define EXT_CSD_STROBE_SUPPORT         184     /* RO */
>  #define EXT_CSD_HS_TIMING              185     /* R/W */
>  #define EXT_CSD_POWER_CLASS            187     /* R/W */
>  #define EXT_CSD_REV                    192     /* RO */
> @@ -380,12 +381,14 @@ struct _mmc_csd {
>  #define EXT_CSD_CARD_TYPE_HS400_1_2V   (1<<7)  /* Card can run at 200MHz DDR, 1.2V */
>  #define EXT_CSD_CARD_TYPE_HS400                (EXT_CSD_CARD_TYPE_HS400_1_8V | \
>                                          EXT_CSD_CARD_TYPE_HS400_1_2V)
> +#define EXT_CSD_CARD_TYPE_HS400ES      (1<<8)  /* Card can run at HS400ES */
>
>  #define EXT_CSD_BUS_WIDTH_1    0       /* Card is in 1 bit mode */
>  #define EXT_CSD_BUS_WIDTH_4    1       /* Card is in 4 bit mode */
>  #define EXT_CSD_BUS_WIDTH_8    2       /* Card is in 8 bit mode */
>  #define EXT_CSD_DDR_BUS_WIDTH_4        5       /* Card is in 4 bit DDR mode */
>  #define EXT_CSD_DDR_BUS_WIDTH_8        6       /* Card is in 8 bit DDR mode */
> +#define EXT_CSD_BUS_WIDTH_STROBE BIT(7)        /* Enhanced strobe mode */
>
>  #define EXT_CSD_TIMING_BC      0       /* Backwards compatility */
>  #define EXT_CSD_TIMING_HS      1       /* High speed */
> --
> 2.3.7
>
>

Kind regards
Uffe
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