On 5 October 2016 at 22:03, Rob Herring [off-list ref] wrote:

On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson [off-list ref] wrote:

quoted

On 23 September 2016 at 22:01, Zach Brown [off-list ref] wrote:

quoted

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 <redacted>
---
 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.

If a controller has a capability register and it lies (perhaps the
board has limitations that the SoC does not), then you may need to
disable a feature.

I understand, although the SDHCI capabilities register is broken for
most SDHCI variants. In principle, we would more or less have to add a
*-broken binding for each bit in that register. I don't like that!

Maybe a better option is to add a "sdhci-cap-broken" or perhaps
"sdhci-cap-speed-modes-broken", which tells the driver to not rely on
the capabilities register and instead find out what *is* supported by
looking at the other mmc generic DT bindings.

What do you think of that?

Kind regards
Uffe
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