Re: [PATCH] mmc: core: Fix access to HS400-ES devices

Doug Anderson
2017-03-01T23:33:37Z

Hi,

On Wed, Mar 1, 2017 at 2:11 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> HS400-ES devices fail to initialize with the following error messages.
>
> mmc1: power class selection to bus width 8 ddr 0 failed
> mmc1: error -110 whilst initialising MMC card
>
> This was seen on Samsung Chromebook Plus. Code analysis points to
> commit 3d4ef329757c ("mmc: core: fix multi-bit bus width without
> high-speed mode"), which attempts to set the bus width for all but
> HS200 devices unconditionally. However, for HS400-ES, the bus width
> is already selected.
>
> Cc: Anssi Hannula <anssi.hannula@bitwise.fi>
> Cc: Douglas Anderson <dianders@chromium.org>
> Cc: Brian Norris <briannorris@chromium.org>
> Fixes: 3d4ef329757c ("mmc: core: fix multi-bit bus width ...")
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
> drivers/mmc/core/mmc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 7fd722868875..b502601df228 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1730,7 +1730,7 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
> err = mmc_select_hs400(card);
> if (err)
> goto free_card;
> - } else {
> + } else if (!mmc_card_hs400es(card)) {
> /* Select the desired bus width optionally */
> err = mmc_select_bus_width(card);
> if (err > 0 && mmc_card_hs(card)) {

Right, so the key point here is that for normal hs400 we hit the
"mmc_card_hs200()" check above because hs400 transitions through
hs200. ...but for hs400es we don't do that transition (we jump
straight to hs400-es), so we need an extra case to avoid this
problematic mmc_select_bus_width().

Reviewed-by: Douglas Anderson <dianders@chromium.org>

-Doug