linux-kernel - Re: [PATCH 2/4] mmc: tegra: fix reporting of base clock frequency

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Date:	Tue, 15 Apr 2014 12:36:07 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Chris Ball <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	linux-tegra@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mmc: tegra: fix reporting of base clock frequency

On Tue, Apr 15, 2014 at 11:25 AM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 04/14/2014 07:42 PM, Andrew Bresticker wrote:
>> Tegra SDHCI controllers, by default, report a base clock frequency
>> of 208Mhz in SDHCI_CAPABILTIES which may or may not be equal to the
>> actual base clock frequency.
>
> Some explanation of why this "may or may not be equal to the actual base
> clock frequency" would be nice.
>
> Presumably, it's because the clock frequency is supplied by the clock
> controller module, and configuring that happens externally to the SD
> controller, so the SD HW has no knowledge of the actual frequency, and
> hence simply reports a hard-coded maximum possible clock frequency?

Correct.  I'll fix up the commit message.

>
>> While this can be overridden by setting
>> BASE_CLK_FREQ in VENDOR_CLOCK_CTRL on Tegra30 and later SoCs, just
>> set SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN and supply a get_max_clock()
>> callback to get the actual rate of the base clock.
>
> It's not clear to me from the function name that
> sdhci_pltfm_clk_get_max_clock() simply calls clk_get() on the actual
> clock. It might be nice to mention that in the commit description.
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