[PATCH v3 3/9] mmc: sdhci: enable CMD23 for multi-block transfers

[Kathpalia, Tanmay]

On 7/5/2026 11:37 AM, Eric Chung wrote:
> Enable the host controller's support for the CMD23 (SET_BLOCK_COUNT)
> command to manage multi-block read/write operations. This allows the
> MMC core to use CMD23 in preference to the legacy CMD18/CMD25 plus
> CMD12 sequence, reducing command overhead and improving I/O
> performance on multi-block transfers.
The commit message claims this enables "host controller" support, but the
changes are entirely in the MMC core (mmc.c) and header. No SDHCI host
driver sets MMC_CAP_CMD23 in this patch. mmc_write_blocks() in
mmc_write.c is not touched. CMD25 still always follows with CMD12.

>
> Signed-off-by: Eric Chung <eric.chung at riscstar.com>
>
> ---
> v3:
> - Avoid to use quirk to enable CMD23. Use capability instead.
> ---
>   drivers/mmc/mmc.c | 18 ++++++++++++++----
>   include/mmc.h     |  6 +++++-
>   2 files changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
> index f0e38efb262..bc8e9ee6d1c 100644
> --- a/drivers/mmc/mmc.c
> +++ b/drivers/mmc/mmc.c
> @@ -461,6 +461,14 @@ static int mmc_read_blocks(struct mmc *mmc, void *dst, lbaint_t start,
>   	struct mmc_cmd cmd;
>   	struct mmc_data data;
>   
> +	if (mmc->host_caps & MMC_CAP_CMD23) {
> +		cmd.cmdidx = MMC_CMD_SET_BLOCK_COUNT;
> +		cmd.cmdarg = blkcnt & 0x0000ffff;
> +		cmd.resp_type = MMC_RSP_R1;
> +		if (mmc_send_cmd(mmc, &cmd, NULL))
> +			return 0;
> +	}
> +

CMD23 is only meaningful before CMD18 (multi-block read). Sending it before
CMD17 (single block, blkcnt == 1) is undefined per the SD spec, which
states: "SET_BLOCK_COUNT - Specify block count for CMD18 and CMD25."

The guard must be:
if (blkcnt > 1 && (mmc->host_caps & MMC_CAP_CMD23)) {

>   	if (blkcnt > 1)
>   		cmd.cmdidx = MMC_CMD_READ_MULTIPLE_BLOCK;
>   	else
> @@ -481,7 +489,7 @@ static int mmc_read_blocks(struct mmc *mmc, void *dst, lbaint_t start,
>   	if (mmc_send_cmd(mmc, &cmd, &data))
>   		return 0;
>   
> -	if (blkcnt > 1) {
> +	if (blkcnt > 1 && !(mmc->host_caps & MMC_CAP_CMD23)) {
>   		if (mmc_send_stop_transmission(mmc, false)) {
>   #if !defined(CONFIG_XPL_BUILD) || defined(CONFIG_SPL_LIBCOMMON_SUPPORT)
>   			log_err("mmc fail to send stop cmd\n");
> @@ -1436,6 +1444,8 @@ static int sd_get_capabilities(struct mmc *mmc)
>   
>   	if (mmc->scr[0] & SD_DATA_4BIT)
>   		mmc->card_caps |= MMC_MODE_4BIT;
> +	if (!(mmc->scr[0] & SD_SCR_CMD23_SUPPORT))
> +		mmc->host_caps &= ~MMC_CAP_CMD23;

Clearing CMD23 capability when the card does not advertise support via
SCR[33] only for SD cards via sd_get_capabilities()but for eMMC the
MMC_CAP_CMD23 flag set by the host driver will remain unconditionally.
Similar handing should be done in mmc_get_capabilities().

>   
>   	/* Version 1.0 doesn't support switching */
>   	if (mmc->version == SD_VERSION_1_0)
> @@ -2963,9 +2973,9 @@ int mmc_get_op_cond(struct mmc *mmc, bool quiet)
>   		return err;
>   
>   #ifdef CONFIG_MMC_QUIRKS
> -	mmc->quirks = MMC_QUIRK_RETRY_SET_BLOCKLEN |
> -		      MMC_QUIRK_RETRY_SEND_CID |
> -		      MMC_QUIRK_RETRY_APP_CMD;
> +	mmc->quirks |= MMC_QUIRK_RETRY_SET_BLOCKLEN |
> +		       MMC_QUIRK_RETRY_SEND_CID |
> +		       MMC_QUIRK_RETRY_APP_CMD;

Unrelated to CMD23 support.
>   #endif
>   
>   	err = mmc_power_cycle(mmc);
> diff --git a/include/mmc.h b/include/mmc.h
> index 9509c9e9543..b663da71019 100644
> --- a/include/mmc.h
> +++ b/include/mmc.h
> @@ -67,6 +67,7 @@ struct bd_info;
>   #define MMC_CAP_NONREMOVABLE	BIT(14)
>   #define MMC_CAP_NEEDS_POLL	BIT(15)
>   #define MMC_CAP_CD_ACTIVE_HIGH  BIT(16)
> +#define MMC_CAP_CMD23		BIT(17)
>   
>   #define MMC_MODE_8BIT		BIT(30)
>   #define MMC_MODE_4BIT		BIT(29)
> @@ -141,6 +142,8 @@ static inline bool mmc_is_tuning_cmd(uint cmdidx)
>   #define SD_HIGHSPEED_BUSY	0x00020000
>   #define SD_HIGHSPEED_SUPPORTED	0x00020000
>   
> +#define SD_SCR_CMD23_SUPPORT	BIT(1)
> +
>   #define UHS_SDR12_BUS_SPEED	0
>   #define HIGH_SPEED_BUS_SPEED	1
>   #define UHS_SDR25_BUS_SPEED	1
> @@ -343,7 +346,8 @@ static inline bool mmc_is_tuning_cmd(uint cmdidx)
>   
>   #define MMC_QUIRK_RETRY_SEND_CID	BIT(0)
>   #define MMC_QUIRK_RETRY_SET_BLOCKLEN	BIT(1)
> -#define MMC_QUIRK_RETRY_APP_CMD	BIT(2)
> +#define MMC_QUIRK_RETRY_APP_CMD		BIT(2)
> +#define MMC_QUIRK_BLK_CMD23		BIT(3)

BLK_CMD23 quirk leftover from the previous patch

Regards,
Tanmay Kathpalia