linux-kernel - Re: [PATCH] mmc: tegra: Disable UHS-I modes for tegra30

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Date:	Tue, 10 May 2016 10:34:48 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-mmc@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lucas Stach <dev@...xeye.de>
Subject: Re: [PATCH] mmc: tegra: Disable UHS-I modes for tegra30

On 05/10/2016 10:13 AM, Jon Hunter wrote:
>
> On 09/05/16 16:15, Jon Hunter wrote:
>> Support for SD cards is not working on the Tegra30 Beaver board and on
>> boot the following error message is seen if an SD card is present:
>>
>>   mmc0: error -110 whilst initialising SD card
>>
>> In addition to this, Tegra30 is also randomly hanging during system
>> suspend when entering and is caused by the Tegra SDHCI driver. Similar
>> issues have been seen on the Tegra124 Jetson TK1 and are linked to the
>> UHS-I tuning sequence. Disabling the UHS-I modes for Tegra30 fixes SD
>> card support and prevents any hangs from occurring when entering system
>> suspend. Therefore, disable the UHS-I modes for Tegra30 for now until
>> we can correct the tuning sequence for Tegra.
>>
>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>> ---
>>   drivers/mmc/host/sdhci-tegra.c | 4 ----
>>   1 file changed, 4 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
>> index bcc0de47fe7e..24c33aee8e7c 100644
>> --- a/drivers/mmc/host/sdhci-tegra.c
>> +++ b/drivers/mmc/host/sdhci-tegra.c
>> @@ -347,10 +347,6 @@ static const struct sdhci_pltfm_data sdhci_tegra30_pdata = {
>>
>>   static const struct sdhci_tegra_soc_data soc_data_tegra30 = {
>>   	.pdata = &sdhci_tegra30_pdata,
>> -	.nvquirks = NVQUIRK_ENABLE_SDHCI_SPEC_300 |
>
> Ugh ... looks like I may have been a bit trigger happy with sending this
> patch. I should not have removed the above line. However, it seems that
> if I don't then the problem with the SD not initialising persists. So
> this implies that something else is going on here with this particular
> SD card. Furthermore, I have seen that another tegra30-beaver is
> initialising the SD card fine on kernelci.org and it seems this is
> working for Lucas too.
>
> Plus in suspend I have not seen the mmc timeout warning that I was
> seeing on tegra114/124 when they were failing. That also implies a
> different problem.
>
> Stephen, for your u-boot testing, do you are set the bit in the vendor
> misc register to enable version 3.0 support for sdhci on tegra30? This
> is what the above quirk is doing (and has done so for a very long time).

I don't see anything in the U-Boot driver that is equivalent to the 
kernel's NVQUIRK_ENABLE_SDHCI_SPEC_300. I assume that means the 
controller advertises an early spec version when in U-Boot, which simply 
means U-Boot doesn't know to take advantage of any faster transfer modes 
enabled by later specification versions, but I'm not entirely sure what 
effect the following kernel code has on the HW:

> 	/* Erratum: Enable SDHCI spec v3.00 support */
> 	if (soc_data->nvquirks & NVQUIRK_ENABLE_SDHCI_SPEC_300)
> 		misc_ctrl |= SDHCI_MISC_CTRL_ENABLE_SDHCI_SPEC_300;

Perhaps the kernel driver should pulse the controller's CAR reset signal 
in probe() to ensure that the HW is in a known state?