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

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Date:	Tue, 10 May 2016 11:49:41 -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 11:16 AM, Jon Hunter wrote:
>
> On 10/05/16 17:34, Stephen Warren wrote:
>> On 05/10/2016 10:13 AM, Jon Hunter wrote:
>
> [snip]
>
>>> 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;
>
> Do you see it touch the SDHCI_TEGRA_VENDOR_MISC_CTRL register?

Not at all. For reference, the register is defined in 
arch/arm/include/asm/arch-tegra/tegra_mmc.h as venmiscctl, and that 
symbol isn't referenced anywhere.