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SubjectRe: [PATCH] mmc: core: improve rationality of bus width setting for HS400es
On 9 July 2018 at 08:47, Hongjie Fang <hongjiefang@asrmicro.com> wrote:
> mmc_select_hs400es() calls mmc_select_bus_width() which will try to
> set 4bit transfer mode if fail to set 8bit mode. The problem is that
> the bus width should not be set to 4bit in HS400es mode.

I guess it fails because there is something wrong. Can you please
elaborate under what circumstance the problem occurs?

>
> Signed-off-by: Hongjie Fang <hongjiefang@asrmicro.com>
> ---
> drivers/mmc/core/mmc.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 4466f5d..94c3cc5 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1337,9 +1337,28 @@ static int mmc_select_hs400es(struct mmc_card *card)
> if (err)
> goto out_err;
>
> - err = mmc_select_bus_width(card);
> - if (err < 0)
> + /* Switch card to 8 bit mode */
> + err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> + EXT_CSD_BUS_WIDTH,
> + EXT_CSD_BUS_WIDTH_8,
> + card->ext_csd.generic_cmd6_time);
> + if (err) {
> + pr_err("%s: switch to 8 bit mode for hs400es failed, err:%d\n",
> + mmc_hostname(host), err);
> + goto out_err;
> + }
> +
> + mmc_set_bus_width(host, MMC_BUS_WIDTH_8);
> +
> + if (!(host->caps & MMC_CAP_BUS_WIDTH_TEST))
> + err = mmc_compare_ext_csds(card, MMC_BUS_WIDTH_8);
> + else
> + err = mmc_bus_test(card, MMC_BUS_WIDTH_8);
> + if (err) {
> + pr_err("%s: test 8 bit mode for hs400es failed, err:%d\n",
> + mmc_hostname(host), err);
> goto out_err;

Lot's open coding, no I don't like it.

Wouldn't it instead be possible to check the return value from
mmc_select_bus_width(), as it should tell what width it manage to
select. Then if it isn't 8-bit, then we should bail out. Does that
work?

> + }
>
> /* Switch card to HS mode */
> err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
> --
> 1.9.1
>

Kind regards
Uffe

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