On Thu, Oct 06, 2016 at 10:03:56AM +0200, Ulf Hansson wrote:
> On 5 October 2016 at 22:03, Rob Herring <robh...@kernel.org> wrote:
> > On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hans...@linaro.org> wrote:
> >> On 23 September 2016 at 22:01, Zach Brown <zach.br...@ni.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.br...@ni.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.
> > 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
"sdhci-cap-broken" seems too aggressive. There might only be one capability
that the register incorrectly advertises.
"sdhci-cap-speed-modes-broken" makes more sense and I will re-create this patch
set using that idea.