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

[유한경 <hankyung.yu@lge.com>]

Hi I'm Hankyung Yu

I will answer instead Chanho Min

HS200 mode right thing to support less than 52Mhz

However CLK <-> DATA delay timing is dependent on the clock.

So only lower clock without adjusting the timing and mode of a control h/w
ever the problem may occur.

So change the operating mode and to lower the clock.


-----Original Message-----
From: Adrian Hunter [mailto:adrian.hunter@intel.com] 
Sent: Tuesday, October 28, 2014 10:24 PM
To: Chanho Min
Cc: Chris Ball; Ulf Hansson; Seungwon Jeon; Jaehoon Chung; linux-
mmc@vger.kernel.org; linux-kernel@vger.kernel.org; HyoJun Im; gunho.lee@lge.
com; Hankyung Yu
Subject: Re: [PATCH] mmc:core: fix hs400 timing selection

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,
>