On 4 July 2018 at 17:07, Stefan Agner <stefan@xxxxxxxx> wrote: > If pinctrl nodes for 100/200MHz are missing, the controller should > not select any mode which need signal frequencies 100MHz or higher. > To prevent such speed modes the driver currently uses the quirk flag > SDHCI_QUIRK2_NO_1_8_V. This works nicely for SD cards since 1.8V > signaling is required for all faster modes and slower modes use 3.3V > signaling only. > > However, there are eMMC modes which use 1.8V signaling and run below > 100MHz, e.g. DDR52 at 1.8V. With using SDHCI_QUIRK2_NO_1_8_V this > mode is prevented. When using a fixed 1.8V regulator as vqmmc-supply > the stack has no valid mode to use. In this tenuous situation the > kernel continuously prints voltage switching errors: > mmc1: Switching to 3.3V signalling voltage failed > > Avoid using SDHCI_QUIRK2_NO_1_8_V and prevent faster modes by > altering the SDHCI capability register. With that the stack is able > to select 1.8V modes even if no faster pinctrl states are available: > # cat /sys/kernel/debug/mmc1/ios > ... > timing spec: 8 (mmc DDR52) > signal voltage: 1 (1.80 V) > ... > > Link: http://lkml.kernel.org/r/20180628081331.13051-1-stefan@xxxxxxxx > Signed-off-by: Stefan Agner <stefan@xxxxxxxx> I am fine with this. Do you want me to apply this for now, to get it tested? I guess its also material for stable and as fix? In regards to the printed warning, it sounds to me like a different issue, which we can solve on top. Right? [...] Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
