mmc: sdhci-of-arasan: Don't power PHY w/ slow/no clock
PHY intended to be used with the Arasan SDHCI 5.1 controller has trouble turning on when the card clock is slow or off. Strangely these problems appear to show up consistently on some boards while other boards work fine, but on the boards where it shows up the problem reproduces 100% of the time and is quite consistent in its behavior. These problems can be fixed by always making sure that we power on the PHY (and turn on its DLL) when the card clock is faster than about 50 MHz. Once on, we need to make sure that we never power down the PHY / turn off its DLL until the clock is faster again. We'll add logic for handling this into the sdhci-of-arasan driver. Note that right now the only user of a PHY in the sdhci-of-arasan driver is arasan,sdhci-5.1. It's presumed that all arasan,sdhci-5.1 PHY implementations need this workaround, so the logic is only contingent on having a PHY to control. If future Arasan controllers don't have this problem we can add code to decide if we want this flow or not. Also note that we check for slow clocks by checking for <= 400 kHz rather than checking for 50 MHz. This keeps things the most consistent and also means we can power the PHY on at max speed (where the DLL will lock fastest). Presumably anyone who intends to run with a card clock of < 50 MHz and > 400 kHz will be running on a device where this problem is fixed anyway. I believe this brings some resolution to the problems reported before. See the commit 6fc09244 ("mmc: sdhci-of-arasan: Revert: Always power the PHY off/on when clock changes"). Signed-off-by: NDouglas Anderson <dianders@chromium.org> Acked-by: NAdrian Hunter <adrian.hunter@intel.com> Reviewed-by: NShawn Lin <shawn.lin@rock-chips.com> Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>
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