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

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Date:	Tue, 10 May 2016 18:16:08 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
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 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?

The TRM states ...

"SDMMC_SPARE0[4] : When set, SD3.0 support is advertised in
SDMMC_SLOT_INTERRUPT_STATUS_0_SPECIFICATION_VERSION_NUMBER Otherwise,
only SD2.0 support is advertised"

So I *believe* this means that the sdhci version will now appear as 3.0
and so the host->version == SDHCI_SPEC_300. There are many places in the
sdhci driver where it is checking ...

 if (host->version >= 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?

I will take a look.

Jon