On 4 July 2018 at 17:18, Stefan Agner <stefan@xxxxxxxx> wrote: > On 04.07.2018 17:07, Stefan Agner 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> >> --- > > Btw, I still get the switching error once during boot-up: > mmc1: Switching to 3.3V signalling voltage failed I guess the this happens then also at system resume? The core tries first with 3.3 then if it fails, it continues with 1.8V, etc. > > This is due to the call from mmc_set_initial_signal_voltage. It is a bit > unfortunate since this is printed as a warning. Not sure if that could > be prevented somehow? Seems like SDHCI_SIGNALING_330 should not be set, unless 3.3V I/O is supported. That should avoid SDHCI from trying and instead just returning an error code immediately. This seems like a generic issues for all SDHCI variant drivers. [...] 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
