Re: [PATCH] mmc:core: fix hs400 timing selection

[Adrian Hunter <adrian.hunter@intel.com>]

On 22/10/14 05:55, Chanho Min wrote:
> According to JEDEC v5.01 spec (6.6.5), In order to switch to HS400 mode,
> host should perform the following steps.
> 
>  1. HS200 mode selection completed
>  2. Set HS_TIMING to 0x01(High Speed)
>  3. Host changes frequency to =< 52MHz
>  4. Set the bus width to DDR 8bit (CMD6)
>  5. Host may read Driver Strength (CMD8)
>  6. Set HS_TIMING to 0x03 (HS400)
> 
> In current implementation, the order of 2 and 3 is reversed.

But HS200 mode supports running at speeds less than 52 MHz whereas
High Speed mode does not support running at speeds greater than
52 MHz.

So the switch command might succeed, but the subsequent send_status
command (see __mmc_switch) could be expected to fail unless the frequency is
changed first.

> The HS_TIMING field should be set to 0x1 before the clock frequency
> is set to a value not greater than 52 MHz. Otherwise, Initialization of
> timing can be failed. Also, the host contoller's UHS timing mode should
> be set to DDR50 after the bus width is set to DDR 8bit.
> 
> Signed-off-by: Hankyung Yu <hankyung.yu@lge.com>
> Signed-off-by: Chanho Min <chanho.min@lge.com>
> ---
>  drivers/mmc/core/mmc.c |   13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index a301a78..52f78e0 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1061,9 +1061,6 @@ static int mmc_select_hs400(struct mmc_card *card)
>  	 * Before switching to dual data rate operation for HS400,
>  	 * it is required to convert from HS200 mode to HS mode.
>  	 */
> -	mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
> -	mmc_set_bus_speed(card);
> -
>  	err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>  			   EXT_CSD_HS_TIMING, EXT_CSD_TIMING_HS,
>  			   card->ext_csd.generic_cmd6_time,
> @@ -1074,6 +1071,14 @@ static int mmc_select_hs400(struct mmc_card *card)
>  		return err;
>  	}
>  
> +	/*
> +	 * According to JEDEC v5.01 spec (6.6.5), Clock frequency should
> +	 * be set to a value not greater than 52MHz after the HS_TIMING
> +	 * field is set to 0x1.
> +	 */
> +	mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
> +	mmc_set_bus_speed(card);
> +
>  	err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>  			 EXT_CSD_BUS_WIDTH,
>  			 EXT_CSD_DDR_BUS_WIDTH_8,
> @@ -1084,6 +1089,8 @@ static int mmc_select_hs400(struct mmc_card *card)
>  		return err;
>  	}
>  
> +	mmc_set_timing(card->host, MMC_TIMING_MMC_DDR52);
> +
>  	err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>  			   EXT_CSD_HS_TIMING, EXT_CSD_TIMING_HS400,
>  			   card->ext_csd.generic_cmd6_time,
>