[U-Boot] [PATCH] mmc: Do not poll using CMD13 when changing timing

[Jean-Jacques Hiblot]

On 06/02/2019 14:11, Marek Vasut wrote:
> When using CMD6 to switch eMMC card timing from HS200/HS400 to HS/legacy,
> do not poll for the completion status using CMD13, but rather wait 50mS.
>
> Once the card receives the CMD6 and starts executing it, the bus is in
> undefined state until both the card finishes executing the command and
> until the controller switches the bus to matching timing configuration.
> During this time, it is not possible to transport any commands or data
> across the bus, which includes the CMD13.
>
> Signed-off-by: Marek Vasut <marek.vasut+renesas at gmail.com>
> Cc: Jaehoon Chung <jh80.chung at samsung.com>
> ---
> NOTE: Linux does the same thing.
> ---
>   drivers/mmc/mmc.c | 28 ++++++++++++++++++++--------
>   1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
> index c7730c9233..ababacf65a 100644
> --- a/drivers/mmc/mmc.c
> +++ b/drivers/mmc/mmc.c
> @@ -720,7 +720,8 @@ static int mmc_send_ext_csd(struct mmc *mmc, u8 *ext_csd)
>   	return err;
>   }
>   
> -int mmc_switch(struct mmc *mmc, u8 set, u8 index, u8 value)
> +static int __mmc_switch(struct mmc *mmc, u8 set, u8 index, u8 value,
> +			bool send_status)
>   {
>   	struct mmc_cmd cmd;
>   	int timeout = 1000;
> @@ -736,19 +737,29 @@ int mmc_switch(struct mmc *mmc, u8 set, u8 index, u8 value)
>   	while (retries > 0) {
>   		ret = mmc_send_cmd(mmc, &cmd, NULL);
>   
> -		/* Waiting for the ready status */
> -		if (!ret) {
> -			ret = mmc_send_status(mmc, timeout);
> -			return ret;
> +		if (ret) {
> +			retries--;
> +			continue;
> +		}
> +
> +		if (!send_status) {
> +			mdelay(50);
> +			return 0;
>   		}
>   
> -		retries--;
> +		/* Waiting for the ready status */
> +		return mmc_send_status(mmc, timeout);
>   	}
>   
>   	return ret;
>   
>   }
>   
> +int mmc_switch(struct mmc *mmc, u8 set, u8 index, u8 value)
> +{
> +	return __mmc_switch(mmc, set, index, value, true);
> +}
> +
>   #if !CONFIG_IS_ENABLED(MMC_TINY)
>   static int mmc_set_card_speed(struct mmc *mmc, enum bus_mode mode,
>   			      bool hsdowngrade)
> @@ -780,8 +791,9 @@ static int mmc_set_card_speed(struct mmc *mmc, enum bus_mode mode,
>   	default:
>   		return -EINVAL;
>   	}
> -	err = mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
> -			 speed_bits);
> +
> +	err = __mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
> +			   speed_bits, !hsdowngrade);
>   	if (err)
>   		return err;
>   
Reviewed-by: Jean-Jacques Hiblot <jjhiblot at ti.com>