Re: [RFC 1/2] sdhci: Add device tree property sd-broken-highspeed
From: Ulf Hansson
Date: Wed Oct 05 2016 - 14:41:49 EST
On 23 September 2016 at 22:01, Zach Brown <zach.brown@xxxxxx> 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@xxxxxx>
> 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"