linux-kernel - Re: [PATCH] mmc:core: fix hs400 timing selection

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Date:	Tue, 28 Oct 2014 13:38:11 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Chanho Min <chanho.min@....com>, Chris Ball <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>
Cc:	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	HyoJun Im <hyojun.im@....com>, gunho.lee@....com,
	Hankyung Yu <hankyung.yu@....com>, CPGS <cpgs@...sung.com>
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@....com>
> Signed-off-by: Chanho Min <chanho.min@....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,
> 

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