[PATCH] imx: kontron-sl-mx8mm: Fix SD card IO voltage level

[Frieder Schrempf]

Hi Marek,

On 25.01.23 18:15, Marek Vasut wrote:
> On 1/25/23 14:41, Frieder Schrempf wrote:
>> From: Frieder Schrempf <frieder.schrempf at kontron.de>
> 
> Subject tags should be ARM: dts: imx:

Ok, how do I know? Because "git log arch/arm/dts" shows me that
"<platform>: <board>:" is used quite often and it's what I used in the
past. But I'm happy to change it if "ARM: dts: imx:" is the way the
prefix should look like.

> 
>> The LDO5 of the PCA9450 PMIC can be switched between two different
>> voltage settings (defaulting to 1.8V and 3.3V) using an external
>> signal SD_VSEL that is connected to the VSELECT signal of the SD
>> card interface.
>>
>> As the regulator driver can't deal with both LDO registers (LDO5CTRL_H
>> and LDO5CTRL_L) it only uses one of them, which means reading the
>> voltage from the regulator can potentially return a value that does not
>> reflect the actual state of the LDO5 output.
> 
> Can you fix the regulator driver ?

So far, I didn't see a way how to do it, but with your suggestion below
it might work.

> 
>> In our case, after booting U-Boot we read 1.8V from the regulator
>> while in fact as the VSELECT signal is still low the regulator outputs
>> 3.3V. This confusion causes the MMC driver to think it is dealing with
>> a 1.8V-only device. This in turn leads to SD cards being addressed
>> with 1.8V IO levels even if UHS support is not available or disabled.
>>
>> Some cards with UHS support still work even if they are addressed
>> with 1.8V levels in non-UHS modes, but a lot of cards also fail with
>> timeout errors like:
>>
>>    Card did not respond to voltage select! : -110
>>
>> As a workaorund we disable the vqmmc regulator for now so we can make
>> sure no wrong values are read from the regulator. The switching
>> between 1.8V and 3.3V still works as the ESDHC driver sets the
>> VSELECT signal accordingly.
>>
>> Signed-off-by: Frieder Schrempf <frieder.schrempf at kontron.de>
>> ---
>> By the way: I suspect that other boards using the PCA9450 might also
>> be affected
>> by this. I didn't find a nice generic solution so far. It would be
>> possible to
>> patch the pca9450 driver to use the PCA9450_LDO5CTRL_L instead of the
>> PCA9450_LDO5CTRL_H register for LDO5. This would fix this particular
>> case,
>> but still not the root problem of the regulator driver returning wrong
>> values.
>> So if anyone got some idea how to properly handle this, let me know.
>> The same issue is also present in Linux. While I didn't notice any
>> problems
>> with the SD card being addressed with incorrect voltage levels so far,
>> reading the regulator doesn't return the correct value if VSELECT is low.
> 
> Configure VSELECT pinmux such that it is a function, as it is right now,
> MX8MP_IOMUXC_GPIO1_IO04__USDHC2_VSELECT or similar, (so SD controller
> driver can operate the pin via SD controller), but set SION bit so GPIO
> controller can read its state (activate bit 30), i.e.:
> MX8MP_IOMUXC_GPIO1_IO04__USDHC2_VSELECT 0x40000004
> 
> Use sd-vsel-gpios property of PMIC, claim the VSELECT as GPIO in PMIC
> driver (this won't change pinmux, the pin would still be configured as
> function, but SION bit would allow you to read its state), read its
> state, and return the correct LDO5CTRL_H/LDO5CTRL_L value based on that.

Good idea, I will try that.

> 
> If this works, then:
>     arm64: dts: imx8mp: Drop sd-vsel-gpios from *
> Linux kernel patches should not be applied.

Yes, but we could also just revert this change once the fix suggested
above works and is in place. Until then the sd-vsel-gpios doesn't do
anything.

Thanks
Frieder