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

From: Ulf Hansson
Date: Wed May 04 2016 - 08:02:26 EST

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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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