On Wed, Oct 05, 2016 at 03:03:44PM -0500, Rob Herring wrote: > On Wed, Oct 5, 2016 at 1:33 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > > 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. > > 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. That's precisely the case here. This is a board-level problem, not a card or controller problem. As Zach mentioned in the cover letter, the trace length between controller and card on some of our boards is too long to meet high-speed timings, even though both card and controller advertise it. Thanks, Julia -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
