Re: MMC error on Exynos4210 board

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On Thu, Jun 19, 2014 at 1:49 AM, Sachin Kamat <spk.linux@xxxxxxxxx> wrote:
> +cc Some relevant guys from Samsung
>
> On Thu, Jun 19, 2014 at 2:12 PM, Tim Kryger <tim.kryger@xxxxxxxxx> wrote:
>> On Wed, Jun 18, 2014 at 8:54 PM, Sachin Kamat <spk.linux@xxxxxxxxx> wrote:
>>
>>>> On Wed, Jun 18, 2014 at 4:33 AM, Sachin Kamat <spk.linux@xxxxxxxxx> wrote:
>>
>>>>> I see the below error on Exynos4210 based Origen board with linux-next
>>>>> (20140618).
>>>>> Reverting the below commit works fine.
>>>>>
>>>>> Commit: 8d02e775a6 "mmc: sdhci: Use mmc core regulator infrastucture"
>>
>>>>>
>>>>> -- [    2.068992] sdhci: Secure Digital Host Controller Interface driver
>>>>> [    2.075059] sdhci: Copyright(c) Pierre Ossman
>>>>> [    2.079762] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12510000[0]'
>>>>> [    2.088021] s3c-sdhci 12510000.sdhci: clock source 2: mmc_busclk.2
>>>>> (50000000 Hz)
>>>>> [    2.095322] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12510000[0]'
>>>>> [    2.103794] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12510000[0]'
>>>>> [    2.112478] s3c-sdhci 12510000.sdhci: No vqmmc regulator found
>>>>> [    2.118117] mmc0: Hardware doesn't report any support voltages.
>>>>> [    2.124004] s3c-sdhci 12510000.sdhci: sdhci_add_host() failed
>>>>> [    2.130080] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12530000[0]'
>>>>> [    2.138352] s3c-sdhci 12530000.sdhci: clock source 2: mmc_busclk.2
>>>>> (16666667 Hz)
>>>>> [    2.145661] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12530000[0]'
>>>>> [    2.154139] of_get_named_gpiod_flags: can't parse gpios property of
>>>>> node '/sdhci@12530000[0]'
>>>>> [    2.162834] s3c-sdhci 12530000.sdhci: No vqmmc regulator found
>>>>> [    2.168464] mmc0: Hardware doesn't report any support voltages.
>>>>> [    2.174349] s3c-sdhci 12530000.sdhci: sdhci_add_host() failed
>>
>>>>> [    2.336148] Waiting for root device /dev/mmcblk0p1...
>>
>>> FYI, the board has a 2.8V fixed regulator supply connected to the MMC.
>>> You may refer to arch/arm/boot/dts/exynos4210-origen.dts for more details.
>>
>> A 2.8v regulator results in mmc->ocr_avail being set to MMC_VDD_27_28
>> | MMC_VDD_28_29.
>>
>> The SDHCI capabilities register only indicates support of three voltage levels
>>   - 1.8v: SDHCI_CAN_VDD_180 => MMC_VDD_165_195
>>   - 3.0v: SDHCI_CAN_VDD_300 => MMC_VDD_29_30 | MMC_VDD_30_31
>>   - 3.3v: SDHCI_CAN_VDD_330 => MMC_VDD_32_33 | MMC_VDD_33_34
>>
>> Even if all capability bits of the host controller were set, there
>> still wouldn't be any overlap.  Thus you see a "Hardware doesn't
>> report any support voltages" message.
>>
>> Previously, this issue was being swept under the rug by cec2e21 mmc:
>> sdhci: Use regulator min/max voltage range according to spec.  That
>> change hacked up the voltage range checks such that with your 2.8v
>> fixed regulator, the driver would believe the host could support
>> MMC_VDD_29_30 | MMC_VDD_30_31 | MMC_VDD_32_33 | MMC_VDD_33_34.  The
>> driver would start down the path of commanding 3.3v-3.4v (the highest
>> voltage range believed to be supported).  At the last second, the
>> driver would see the regulator was fixed and blindly skip over the set
>> voltage operation, saving it from failure.
>>
>> Since my patch eliminates the bogus voltage range checks, your board
>> is now getting caught playing too loose with the SDHCI regulator
>> voltages.
>>
>> Furthermore, the fixed regulator special-case logic that helped hide
>> your issue should also be considered for removal given that fixed
>> regulators now behave properly thanks to c00dc35 regulator: core:
>> Allow regulator_set_voltage for fixed regulators.
>
> Thanks for the detailed explanation. What do you propose to get this fixed?

I'm not really sure of the best path forward.  I suppose you could
modify your device tree to lie about the voltage of the fixed
regulator.  Changing it to 3.0v should allow it to boot up but that is
definitely a hack.  It would be nice if the driver could be extended
to handle the peculiarities of your board in a deliberate manner but
limiting the common sdhci driver to supporting only the three voltages
from the spec also seems sensible.

-Tim
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