Re: [PATCH] mmc: mmc: Fix HS switch failure in mmc_select_hs400()

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

On 26/05/16 08:50, Ziyuan Xu wrote:
> To slove the issue which was found on gru board for hs400.
> 
> [    4.616946] sdhci: Secure Digital Host Controller Interface driver
> [    4.623135] sdhci: Copyright(c) Pierre Ossman
> [    4.722575] sdhci-pltfm: SDHCI platform and OF driver helper
> [    4.730962] sdhci-arasan fe330000.sdhci: No vmmc regulator found
> [    4.737444] sdhci-arasan fe330000.sdhci: No vqmmc regulator found
> [    4.774930] mmc0: SDHCI controller on fe330000.sdhci [fe330000.sdhci] using ADMA
> [    4.980295] mmc0: switch to high-speed from hs200 failed, err:-84
> [    4.986487] mmc0: error -84 whilst initialising MMC card
> 
> We should change HS400 mode selection timing to meet JEDEC
> specification. The JEDEC 5.1 said that change the frequency to <= 52MHZ
> after HS_TIMING switch. Refer to section 6.6.2.3 "HS400" timing mode
> selection:
> Set the "Timing Interface" parameter in the HS_TIMING[185] field of the
> Extended CSD register to 0x1 to switch to High Speed mode and then set
> the clock frequency to a value not greater than 52MHZ.

Do you need a fix also for re-tuning? i.e. does re-tuning work with this
patch? Or do you not need re-tuning?

> 
> Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
> ---
>  drivers/mmc/core/mmc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index b81b08f..8e4d059 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1078,10 +1078,6 @@ static int mmc_select_hs400(struct mmc_card *card)
>  	if (host->caps & MMC_CAP_WAIT_WHILE_BUSY)
>  		send_status = false;
>  
> -	/* Reduce frequency to HS frequency */
> -	max_dtr = card->ext_csd.hs_max_dtr;
> -	mmc_set_clock(host, max_dtr);
> -
>  	/* Switch card to HS mode */
>  	val = EXT_CSD_TIMING_HS;
>  	err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> @@ -1097,6 +1093,10 @@ static int mmc_select_hs400(struct mmc_card *card)
>  	/* Set host controller to HS timing */
>  	mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
>  
> +	/* Reduce frequency to HS frequency */
> +	max_dtr = card->ext_csd.hs_max_dtr;
> +	mmc_set_clock(host, max_dtr);
> +
>  	if (!send_status) {
>  		err = mmc_switch_status(card);
>  		if (err)
>