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    Subject[PATCH 5.4 198/214] mmc: sdhci: Use Auto CMD Auto Select only when v4_mode is true
    Date
    From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>

    commit b3e1ea16fb39fb6e1a1cf1dbdd6738531de3dc7d upstream.

    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@synaptics.com>
    Acked-by: Adrian Hunter <adrian.hunter@intel.com>
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20201015174115.4cf2c19a@xhacker.debian
    Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/mmc/host/sdhci.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    --- a/drivers/mmc/host/sdhci.c
    +++ b/drivers/mmc/host/sdhci.c
    @@ -1162,9 +1162,11 @@ static inline void sdhci_auto_cmd_select
    /*
    * 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);

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