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

[Adrian Hunter <adrian.hunter-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On 29/04/16 05:47, Shawn Lin 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-TNX95d0MmH7DzftRWevZcw@public.gmane.org>

Thanks for doing this.  There are a couple of comments below, but generally
I tend to think you should split out selecting HS400ES as a separate function.

> ---
> 
> 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" : "",
>  			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)))

Could use just "card_type & EXT_CSD_CARD_TYPE_HS400" here

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

I don't think we need this.  Just checking (host->caps & MMC_CAP_8_BIT_DATA)
ought to be enough.  But if you want to play if safe, you could use
mmc_select_bus_width() in advance.

> +		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);

In my view, you should just make a new function: mmc_select_hs400es()

> +	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;
> +
> +		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);

I don't see any need for an error return, so maybe make this return void.
Also, we could put "bool enhanced_strobe" in struct mmc_ios and pass ios
instead of 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;

We shouldn't assume that we are using it, just because it is available.
How about putting "bool enhanced_strobe" in struct mmc_ios and checking that.

> +
> +	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 */
> 

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