Re: [PATCH v2] mmc: sdhci: Use Auto CMD Auto Select only when v4_mode is true

[Ulf Hansson]

On Thu, 15 Oct 2020 at 11:41, Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote:
>
> sdhci-of-dwcmshc meets an eMMC read performance regression with below
> command after commit 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto
> Select support"):
>
> dd if=/dev/mmcblk0 of=/dev/null bs=8192 count=100000
>
> Before the commit, the above command gives 120MB/s
> After the commit, the above command gives 51.3 MB/s
>
> So it looks like sdhci-of-dwcmshc expects Version 4 Mode for Auto
> CMD Auto Select. Fix the performance degradation by ensuring v4_mode
> is true to use Auto CMD Auto Select.
>
> Fixes: 427b6514d095 ("mmc: sdhci: Add Auto CMD Auto Select support")
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>

Applied for fixes and by adding a stable tag, thanks!

Kind regards
Uffe

> ---
> Since v1:
>   - add the performance degradation on sdhci-of-dwcmshc explanation in
>     commit msg
>   - add a comment in the code explaining we require Version 4 Mode because some
>     controllers(e.g sdhci-of-dwcmshc) expect it that way.
>
>  drivers/mmc/host/sdhci.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 592a55a34b58..3561ae8a481a 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1384,9 +1384,11 @@ static inline void sdhci_auto_cmd_select(struct sdhci_host *host,
>         /*
>          * In case of Version 4.10 or later, use of 'Auto CMD Auto
>          * Select' is recommended rather than use of 'Auto CMD12
> -        * Enable' or 'Auto CMD23 Enable'.
> +        * Enable' or 'Auto CMD23 Enable'. We require Version 4 Mode
> +        * here because some controllers (e.g sdhci-of-dwmshc) expect it.
>          */
> -       if (host->version >= SDHCI_SPEC_410 && (use_cmd12 || use_cmd23)) {
> +       if (host->version >= SDHCI_SPEC_410 && host->v4_mode &&
> +           (use_cmd12 || use_cmd23)) {
>                 *mode |= SDHCI_TRNS_AUTO_SEL;
>
>                 ctrl2 = sdhci_readw(host, SDHCI_HOST_CONTROL2);
> --
> 2.28.0
>