linux-kernel - Re: Possible regression with commit 52221610d

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Message-ID: <CAJAp7OgmrEX1XQcwvwf4jzW3eK9TUgde2MQQOp7fOJzvmO=tCQ@mail.gmail.com>
Date:	Sat, 13 Dec 2014 23:22:57 -0800
From:	Bjorn Andersson <bjorn@...o.se>
To:	Tim Kryger <tim.kryger@...il.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Sachin Kamat <spk.linux@...il.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: Possible regression with commit 52221610d

On Tue, Nov 4, 2014 at 7:31 AM, Tim Kryger <tim.kryger@...il.com> wrote:
> On Tue, Nov 4, 2014 at 1:00 AM, Alexandre Courbot <acourbot@...dia.com> wrote:
>> Hi Tim, thanks for your reply!
>>
>> On 11/04/2014 02:28 PM, Tim Kryger wrote:
>>>
>>> On Mon, Nov 3, 2014 at 7:05 PM, Alexandre Courbot <acourbot@...dia.com>
[..]
>>>> After bisecting I tracked commit 52221610dd84dc3e9196554f0292ca9e8ab3541d
>>>> ("mmc: sdhci: Improve external VDD regulator support") as the one that
>>>> introduced this issue, which seems somehow surprising to me since it has
>>>> been around for a while and nobody else complained about this AFAICT.

After some hunting it seems like the recent Qualcomm platforms are
suffering from this as well.

[..]
> In a nutshell, the issue here is that the SDHCI spec demands that VMMC
> be supplied by the controller itself with the specific voltage
> configured using the SDHCI_POWER_CONTROL register but almost nobody
> does this.  Many SoCs omit this capability from their controllers and
> instead rely upon external regulators.  In such cases there isn't
> normally any need to update the voltage bits of the power control
> register.  It sounds like you are saying this isn't true for the
> Tegra114.

Should one interpret your answer as that iff the SDHCI controller
actually follows the specification (and provides the power control)
then as of the introduction of 52221610dd vmmc should no longer be
used for specifying the supply of power to the controller?

Or simply; what is vmmc (in the code) supposed to represent?

Regards,
Bjorn
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