Re: [PATCH v2] mmc: sdhci-esdhc-imx: allow 1.8V modes without 100/200MHz pinctrl states

[Stefan Agner]

On 05.07.2018 15:10, Ulf Hansson wrote:
> 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>
> 
> 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.

--
Stefan

> Kind regards
> Uffe
> 
>> ---
>>  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 */
>> --
>> 2.18.0
>>