linux-kernel - Re: [PATCH v2] mmc: sdhci: Use Auto CMD Auto Select only when v4

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Date:   Thu, 15 Oct 2020 13:14:42 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Chunyan Zhang <zhang.lyra@...il.com>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: sdhci: Use Auto CMD Auto Select only when v4_mode
 is true

On 15/10/20 12:41 pm, Jisheng Zhang 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@...aptics.com>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
> 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);
>