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

[Jean-Jacques Hiblot]

Hi Marek,

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.

Is it something that affects all platforms ?

I've been working on this on TI platforms lately and although I've seen 
the same kind of problems. But they mostly go away If the code handling 
the switch handles the SWITCH_ERROR bit.

JJ
>
> 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;
>