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

[유한경 <hankyung.yu@lge.com>]

Hi I'm Hankyung Yu

I will answer instead Chanho Min

After mmc_set_timing(card->host, MMC_TIMING_MMC_HS); 

Host controller set to SDR transfer

so is to change to a DDR transfer mode.


-----Original Message-----
From: Jaehoon Chung [mailto:jh80.chung@samsung.com] 
Sent: Tuesday, October 28, 2014 1:38 PM
To: Chanho Min; Chris Ball; Ulf Hansson; Seungwon Jeon; Jaehoon Chung
Cc: linux-mmc@vger.kernel.org; linux-kernel@vger.kernel.org; HyoJun Im;
gunho.lee@lge.com; Hankyung Yu; CPGS
Subject: Re: [PATCH] mmc:core: fix hs400 timing selection

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@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);
> +

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,
>