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 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? -- Stefan > drivers/mmc/host/sdhci-esdhc-imx.c | 21 +++++++++------------ > 1 file changed, 9 insertions(+), 12 deletions(-) > > diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c > b/drivers/mmc/host/sdhci-esdhc-imx.c > index 20a420b765b3..e96d969ab2c3 100644 > --- a/drivers/mmc/host/sdhci-esdhc-imx.c > +++ b/drivers/mmc/host/sdhci-esdhc-imx.c > @@ -312,6 +312,15 @@ static u32 esdhc_readl_le(struct sdhci_host *host, int reg) > > if (imx_data->socdata->flags & ESDHC_FLAG_HS400) > val |= SDHCI_SUPPORT_HS400; > + > + /* > + * Do not advertise faster UHS modes if there are no > + * pinctrl states for 100MHz/200MHz. > + */ > + if (IS_ERR_OR_NULL(imx_data->pins_100mhz) || > + IS_ERR_OR_NULL(imx_data->pins_200mhz)) > + val &= ~(SDHCI_SUPPORT_SDR50 | SDHCI_SUPPORT_DDR50 > + | SDHCI_SUPPORT_SDR104 | SDHCI_SUPPORT_HS400); > } > } > > @@ -1157,18 +1166,6 @@ sdhci_esdhc_imx_probe_dt(struct platform_device *pdev, > ESDHC_PINCTRL_STATE_100MHZ); > imx_data->pins_200mhz = pinctrl_lookup_state(imx_data->pinctrl, > ESDHC_PINCTRL_STATE_200MHZ); > - if (IS_ERR(imx_data->pins_100mhz) || > - IS_ERR(imx_data->pins_200mhz)) { > - dev_warn(mmc_dev(host->mmc), > - "could not get ultra high speed state, work on normal mode\n"); > - /* > - * fall back to not supporting uhs by specifying no > - * 1.8v quirk > - */ > - host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V; > - } > - } else { > - host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V; > } > > /* call to generic mmc_of_parse to support additional capabilities */ -- 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
