linux-kernel - Re: [PATCH] mmc: rtsx: fix long reads when clock is prescaled

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Date:   Mon, 16 Aug 2021 15:58:58 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Thomas Hebb <tommyhebb@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ricky Wu <ricky_wu@...ltek.com>,
        Rui Feng <rui_feng@...lsil.com.cn>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-mmc <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH] mmc: rtsx: fix long reads when clock is prescaled

On Sun, 1 Aug 2021 at 13:46, Thomas Hebb <tommyhebb@...il.com> wrote:
>
> For unexplained reasons, the prescaler register for this device needs to
> be cleared (set to 1) while performing a data read or else the command
> will hang. This does not appear to affect the real clock rate sent out
> on the bus, so I assume it's purely to work around a hardware bug.
>
> During normal operation, the prescaler is already set to 1, so nothing
> needs to be done. However, in "initial mode" (which is used for sub-MHz
> clock speeds, like the core sets while enumerating cards), it's set to
> 128 and so we need to reset it during data reads. We currently fail to
> do this for long reads.
>
> This has no functional affect on the driver's operation currently
> written, as the MMC core always sets a clock above 1MHz before
> attempting any long reads. However, the core could conceivably set any
> clock speed at any time and the driver should still work, so I think
> this fix is worthwhile.
>
> I personally encountered this issue while performing data recovery on an
> external chip. My connections had poor signal integrity, so I modified
> the core code to reduce the clock speed. Without this change, I saw the
> card enumerate but was unable to actually read any data.
>
> Writes don't seem to work in the situation described above even with
> this change (and even if the workaround is extended to encompass data
> write commands). I was not able to find a way to get them working.
>
> Signed-off-by: Thomas Hebb <tommyhebb@...il.com>

Applied for next, thanks!

Kind regards
Uffe


>
> ---
>
>  drivers/mmc/host/rtsx_pci_sdmmc.c | 36 ++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/mmc/host/rtsx_pci_sdmmc.c b/drivers/mmc/host/rtsx_pci_sdmmc.c
> index 4ca937415734..58cfaffa3c2d 100644
> --- a/drivers/mmc/host/rtsx_pci_sdmmc.c
> +++ b/drivers/mmc/host/rtsx_pci_sdmmc.c
> @@ -542,9 +542,22 @@ static int sd_write_long_data(struct realtek_pci_sdmmc *host,
>         return 0;
>  }
>
> +static inline void sd_enable_initial_mode(struct realtek_pci_sdmmc *host)
> +{
> +       rtsx_pci_write_register(host->pcr, SD_CFG1,
> +                       SD_CLK_DIVIDE_MASK, SD_CLK_DIVIDE_128);
> +}
> +
> +static inline void sd_disable_initial_mode(struct realtek_pci_sdmmc *host)
> +{
> +       rtsx_pci_write_register(host->pcr, SD_CFG1,
> +                       SD_CLK_DIVIDE_MASK, SD_CLK_DIVIDE_0);
> +}
> +
>  static int sd_rw_multi(struct realtek_pci_sdmmc *host, struct mmc_request *mrq)
>  {
>         struct mmc_data *data = mrq->data;
> +       int err;
>
>         if (host->sg_count < 0) {
>                 data->error = host->sg_count;
> @@ -553,22 +566,19 @@ static int sd_rw_multi(struct realtek_pci_sdmmc *host, struct mmc_request *mrq)
>                 return data->error;
>         }
>
> -       if (data->flags & MMC_DATA_READ)
> -               return sd_read_long_data(host, mrq);
> +       if (data->flags & MMC_DATA_READ) {
> +               if (host->initial_mode)
> +                       sd_disable_initial_mode(host);
>
> -       return sd_write_long_data(host, mrq);
> -}
> +               err = sd_read_long_data(host, mrq);
>
> -static inline void sd_enable_initial_mode(struct realtek_pci_sdmmc *host)
> -{
> -       rtsx_pci_write_register(host->pcr, SD_CFG1,
> -                       SD_CLK_DIVIDE_MASK, SD_CLK_DIVIDE_128);
> -}
> +               if (host->initial_mode)
> +                       sd_enable_initial_mode(host);
>
> -static inline void sd_disable_initial_mode(struct realtek_pci_sdmmc *host)
> -{
> -       rtsx_pci_write_register(host->pcr, SD_CFG1,
> -                       SD_CLK_DIVIDE_MASK, SD_CLK_DIVIDE_0);
> +               return err;
> +       }
> +
> +       return sd_write_long_data(host, mrq);
>  }
>
>  static void sd_normal_rw(struct realtek_pci_sdmmc *host,
> --
> 2.32.0
>