linux-kernel - Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

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Message-ID: <CAPDyKFogDKM86XKo1iQE1KU5HpEic23FD5YQGF9QjSFYBDJn4Q@mail.gmail.com>
Date:   Wed, 5 Oct 2016 20:33:56 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Zach Brown <zach.brown@...com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed

On 23 September 2016 at 22:01, Zach Brown <zach.brown@...com> wrote:
> Certain board configurations can make highspeed malfunction due to
> timing issues. In these cases a way is needed to force the controller
> and card into standard speed even if they otherwise appear to be capable
> of highspeed.
>
> The sd-broken-highspeed property will let the sdhci driver know that
> highspeed will not work.
>
> Signed-off-by: Zach Brown <zach.brown@...com>
> ---
>  Documentation/devicetree/bindings/mmc/mmc.txt | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mmc/mmc.txt b/Documentation/devicetree/bindings/mmc/mmc.txt
> index 8a37782..59332ea 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc.txt
> +++ b/Documentation/devicetree/bindings/mmc/mmc.txt
> @@ -52,6 +52,8 @@ Optional properties:
>  - no-sdio: controller is limited to send sdio cmd during initialization
>  - no-sd: controller is limited to send sd cmd during initialization
>  - no-mmc: controller is limited to send mmc cmd during initialization
> +- sd-broken-highspeed: Highspeed is broken, even if the controller and card
> +  themselves claim they support highspeed.

Regarding a broken card, that is managed via the card quirks and not in DT.

If this is about a controller limitation, we already have the option
to describe what it supports, so we don't need an option to tell what
it *not* supports.

For example "cap-sd-highspeed" tells whether the controller supports
SD high-speed, please use that instead.

>
>  *NOTE* on CD and WP polarity. To use common for all SD/MMC host controllers line
>  polarity properties, we have to fix the meaning of the "normal" and "inverted"
> --
> 2.7.4
>

Kind regards
Uffe