Re: [RFC] mmc: core: Set clock before switching to highspeed mode.

[Shawn Lin <shawn.lin-TNX95d0MmH7DzftRWevZcw@public.gmane.org>]

On 2015/9/5 18:19, Yousong Zhou wrote:
> A SD card with sunxi-mmc can fail with the following error message (RCD for
> response CRC error) when trying to switch to highspeed mode.  Setting the bus
> clock before the access mode switch fixed it.

No, that's wrong!

Before this card is switched to highspeed, it works under identification 
mode(From spec: bus clock <= 400KHz). How could you
raise bus clock to higher clk rate which I _guess_ is 52MHz before you 
notify sd cards to run into highspeed mode?

Althought it works for this card, this patch will not please the other 
cards that they might not reply CMDs any longer including the following 
CMD6.


>
>      [    1.112060] mmc0: host does not support reading read-only switch, assuming write-enable
>      [    1.120203] ehci-platform 1c1c000.usb: irq 31, io mem 0x01c1c000
>      [    1.126527] sunxi-mmc 1c0f000.mmc: smc 0 err, cmd 6, RD RCE !!
>      [    1.132388] sunxi-mmc 1c0f000.mmc: data error, sending stop command
>      [    1.139451] sunxi-mmc 1c0f000.mmc: send stop command failed
>      [    1.145056] mmc0: error -110 whilst initialising SD card
>      [    1.150424] ehci-platform 1c1c000.usb: USB 2.0 started, EHCI 1.00
>      [    1.156533] sunxi-mmc 1c0f000.mmc: smc 0 err, cmd 1, RTO !!
>
> Signed-off-by: Yousong Zhou <yszhou4tech-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>   drivers/mmc/core/sd.c |   10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> index 4e7366a..402a8db 100644
> --- a/drivers/mmc/core/sd.c
> +++ b/drivers/mmc/core/sd.c
> @@ -366,6 +366,11 @@ int mmc_sd_switch_hs(struct mmc_card *card)
>   		return -ENOMEM;
>   	}
>
> +	/*
> +	 * Set bus frequency to match highspeed mode.
> +	 */
> +	mmc_set_clock(card->host, mmc_sd_get_max_clock(card));
> +
>   	err = mmc_sd_switch(card, 1, 0, 1, status);
>   	if (err)
>   		goto out;
> @@ -969,11 +974,6 @@ static int mmc_sd_init_card(struct mmc_host *host, u32 ocr,
>   			goto free_card;
>
>   		/*
> -		 * Set bus speed.
> -		 */
> -		mmc_set_clock(host, mmc_sd_get_max_clock(card));
> -
> -		/*
>   		 * Switch to wider bus (if supported).
>   		 */
>   		if ((host->caps & MMC_CAP_4_BIT_DATA) &&
>


-- 
Best Regards
Shawn Lin