On 05.07.2018 11:48, Ulf Hansson wrote: > 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. Hm, can we resolve this in a generic fashion? E.g something like this in sdhci_setup_host(): if (!regulator_is_supported_voltage(mmc->supply.vqmmc, 3200000, 3450000)) host->flags &= ~SDHCI_SIGNALING_330; -- Stefan -- 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
