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

From: Jaehoon Chung
Date: Tue Oct 28 2014 - 00:38:21 EST


Hi, Chanho.

On 10/22/2014 11:55 AM, 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.
> 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@xxxxxxx>
> Signed-off-by: Chanho Min <chanho.min@xxxxxxx>
> ---
> 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);
> +

I didn't know why timing is set to ddr50.

Best Regards,
Jaehoon Chung

> err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> EXT_CSD_HS_TIMING, EXT_CSD_TIMING_HS400,
> card->ext_csd.generic_cmd6_time,
>

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