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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Mon, 7 Nov 2022 21:13:00 +0100
Message-ID: <CAPDyKFptJkHGaz9zc2G65tyS=2weH7ueV1d_CAszKfAgsqCkAw@mail.gmail.com>
Subject: Re: [PATCH] mmc: core: properly select voltage range without power cycle
To:     Yann Gautier <yann.gautier@foss.st.com>
Cc:     Wolfram Sang <wsa+renesas@sang-engineering.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Kees Cook <keescook@chromium.org>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Shaik Sajida Bhanu <quic_c_sbhanu@quicinc.com>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>, linux-mmc@vger.kernel.org,
        linux-kernel@vger.kernel.org, christophe.kerello@foss.st.com
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On Fri, 28 Oct 2022 at 09:38, Yann Gautier <yann.gautier@foss.st.com> wrote:
>
> In mmc_select_voltage(), if there is no full power cycle, the voltage
> range selected at the end of the function will be on a single range
> (e.g. 3.3V/3.4V). To keep a range around the selected voltage (3.2V/3.4V),
> the mask shift should be reduced by 1.
>
> This issue was triggered by using a specific SD-card (Verbatim Premium
> 16GB UHS-1) on an STM32MP157C-DK2 board. This board cannot do UHS modes
> and there is no power cycle. And the card was failing to switch to
> high-speed mode. When adding the range 3.2V/3.3V for this card with the
> proposed shift change, the card can switch to high-speed mode.
>
> Fixes: ce69d37b7d8f ("mmc: core: Prevent violation of specs while initializing cards")
> Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>

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

Kind regards
Uffe


> ---
>  drivers/mmc/core/core.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 95fa8fb1d45f..c5de202f530a 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1134,7 +1134,13 @@ u32 mmc_select_voltage(struct mmc_host *host, u32 ocr)
>                 mmc_power_cycle(host, ocr);
>         } else {
>                 bit = fls(ocr) - 1;
> -               ocr &= 3 << bit;
> +               /*
> +                * The bit variable represents the highest voltage bit set in
> +                * the OCR register.
> +                * To keep a range of 2 values (e.g. 3.2V/3.3V and 3.3V/3.4V),
> +                * we must shift the mask '3' with (bit - 1).
> +                */
> +               ocr &= 3 << (bit - 1);
>                 if (bit != host->ios.vdd)
>                         dev_warn(mmc_dev(host), "exceeding card's volts\n");
>         }
> --
> 2.25.1
>