linux-kernel - Re: [PATCH 2/3] mmc: sdhci: add quirk to prevent higher speed modes

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Date:   Mon, 2 Jul 2018 16:36:59 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Stefan Agner <stefan@...er.ch>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Haibo Chen <haibo.chen@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        Russell King <rmk+kernel@...linux.org.uk>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mmc: sdhci: add quirk to prevent higher speed modes

On 28 June 2018 at 10:13, Stefan Agner <stefan@...er.ch> wrote:
> Some hosts are capable of running higher speed modes but do not
> have the board support for it. Introduce a quirk which prevents
> the stack from using modes running at 100MHz or faster.

To cap the freq, use the DT property "max-frequency". To enable
certain speed modes, use the corresponding speed mode binding. For
example "sd-uhs-sdr*" and "mmc-hs200*".
Documented in Documentation/devicetree/bindings/mmc/mmc.txt

In case the sdhci cap register, doesn't reflect the board support
properly, such that you may want to disable some speed modes, then you
may benefit from using the DT properties "sdhci-caps*.
Documented in Documentation/devicetree/bindings/mmc/sdhci.txt

Kind regards
Uffe

>
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
>  drivers/mmc/host/sdhci.c | 8 ++++++++
>  drivers/mmc/host/sdhci.h | 2 ++
>  2 files changed, 10 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 1c828e0e9905..8ac257dfaab3 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3749,6 +3749,14 @@ int sdhci_setup_host(struct sdhci_host *host)
>                 }
>         }
>
> +       if (host->quirks2 & SDHCI_QUIRK2_NO_UHS_HS200_HS400) {
> +               host->caps1 &= ~(SDHCI_SUPPORT_SDR104 | SDHCI_SUPPORT_SDR50 |
> +                                SDHCI_SUPPORT_DDR50);
> +
> +               mmc->caps2 &= ~(MMC_CAP2_HSX00_1_8V | MMC_CAP2_HSX00_1_2V |
> +                               MMC_CAP2_HS400_ES);
> +       }
> +
>         if (host->quirks2 & SDHCI_QUIRK2_NO_1_8_V) {
>                 host->caps1 &= ~(SDHCI_SUPPORT_SDR104 | SDHCI_SUPPORT_SDR50 |
>                                  SDHCI_SUPPORT_DDR50);
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index 23966f887da6..cb2433d6d61f 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -450,6 +450,8 @@ struct sdhci_host {
>   * obtainable timeout.
>   */
>  #define SDHCI_QUIRK2_DISABLE_HW_TIMEOUT                        (1<<17)
> +/* Do not support any higher speeds (>50MHz) */
> +#define SDHCI_QUIRK2_NO_UHS_HS200_HS400                        (1<<18)
>
>         int irq;                /* Device IRQ */
>         void __iomem *ioaddr;   /* Mapped address */
> --
> 2.18.0
>