On 5 July 2018 at 16:22, Stefan Agner <[email protected]> wrote: > On 05.07.2018 15:10, Ulf Hansson wrote: >> On 4 July 2018 at 17:07, Stefan Agner <[email protected]> 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/[email protected] >>> Signed-off-by: Stefan Agner <[email protected]> >> >> Thanks, applied for next! Let's see if this turns out okay, then let's >> make it a fix and add a stable tag. >> >> BTW, would you mind looking up the commit it fixes? Or if there is a >> certain stable release we should target. >> > > The quirk SDHCI_QUIRK2_NO_1_8_V has been used if pinctrl were missing > since support has been added for additional pinctrl states (back around > 3.13). > > Fixes: ad93220de7da ("mmc: sdhci-esdhc-imx: change pinctrl state > according to uhs mode") > > I guess it won't apply on older kernels since the code which applies the > quirk has been moved around.
Thanks! I have moved the patch to fixes and added a stable tag, # v4.13+. It applied cleanly on top of that kernel version, if you or anyone else needs it for an older kernel, please post a backported patch. [...] Kind regards Uffe
