Re: Possible regression with commit 52221610d

[Alexandre Courbot <acourbot@nvidia.com>]

On 11/05/2014 12:31 AM, Tim Kryger wrote:
> On Tue, Nov 4, 2014 at 1:00 AM, Alexandre Courbot <acourbot@nvidia.com> wrote:
>> Hi Tim, thanks for your reply!
>>
>> On 11/04/2014 02:28 PM, Tim Kryger wrote:
>>>
>>> On Mon, Nov 3, 2014 at 7:05 PM, Alexandre Courbot <acourbot@nvidia.com>
>>> wrote:
>>>>
>>>> Hi guys,
>>>>
>>>> On the NVIDIA shield (tegra114-roth) platform, I have noticed that MMC
>>>> stopped working completely on recent kernels. MMC devices will not show
>>>> up
>>>> and the message "mmc1: Controller never released inhibit bit(s)." shows
>>>> up
>>>> repeatedly in the console.
>>>>
>>>> After bisecting I tracked commit 52221610dd84dc3e9196554f0292ca9e8ab3541d
>>>> ("mmc: sdhci: Improve external VDD regulator support") as the one that
>>>> introduced this issue, which seems somehow surprising to me since it has
>>>> been around for a while and nobody else complained about this AFAICT.
>>>
>>>
>>> I'm not too familiar with the Nvidia Shield so can you please confirm
>>> the following?
>>>
>>> The controller in the Tegra114 is SDHCI compliant and as such
>>> sdhci_tegra_probe calls sdhci_add_host.  External regulators are
>>> sought in sdhci_add_host with a call to mmc_regulator_get_supply.
>>
>>
>> This is correct.
>>
>>> Since no external regulators are specified in tegra114.dtsi or
>>> tegra114-roth.dts, mmc->supply.vmmc and mmc->supply.vqmmc are set to
>>> -ENODEV.
>>
>>
>> Actually 2 of the MMC nodes in tegra114-roth.dts (for SD card and eMMC) have
>> a vmmc-supply property, so for two of them at least mmc->supply.vmmc is a
>> valid pointer.
>>
>
> I must have been looking at an old version of the file.  Thanks for
> clearing this up.
>
>> As explained above, vmmc is a valid pointer for 2 instances of the MMC
>> controller. Interestingly, if I just remove the "return" line in the
>> IS_ERR() block (without moving it around), the issue also seems to be fixed.
>>
>>>
>>> Can you provide the relevant parts of the log before the problem occurs?
>>
>>
>> There is not much unfortunately ; the only relevant log I have is this:
>>
>> [   12.246022] mmc2: Timeout waiting for hardware interrupt.
>> [   12.264990] mmc2: Controller never released inhibit bit(s).
>>
>> Some hardware interrupt timed out. I don't know much about the MMC
>> subsystem. but could it be because initially the controller is not in a
>> powered-on state, and that return statement causes the function to leave it
>> unpowered?
>
> In a nutshell, the issue here is that the SDHCI spec demands that VMMC
> be supplied by the controller itself with the specific voltage
> configured using the SDHCI_POWER_CONTROL register but almost nobody
> does this.  Many SoCs omit this capability from their controllers and
> instead rely upon external regulators.  In such cases there isn't
> normally any need to update the voltage bits of the power control
> register.  It sounds like you are saying this isn't true for the
> Tegra114.

Thanks for your explanation, it makes sense now.

Looking at other Tegra boards .dts I noticed that SHIELD is the only one 
using a vmmc-supply. Maybe this is the part that is wrong? I wrote this 
DTS and cannot exclude I misread the schematics. Maybe that regulator is 
used for some other (still sdmmc-related) purpose but the actual power 
provider is the controller itself.

If you can confirm that the driver is performing as it should, I will 
look in that direction and revise my DTS.

Thanks!
Alex.