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

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Date:	Tue, 16 Dec 2014 10:18:59 -0800
From:	Bjorn Andersson <bjorn@...o.se>
To:	Tim Kryger <tim.kryger@...il.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	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>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: Possible regression with commit 52221610d

On Mon, Dec 15, 2014 at 10:27 PM, Bjorn Andersson <bjorn@...o.se> wrote:
> On Sun, Dec 14, 2014 at 8:48 PM, Tim Kryger <tim.kryger@...il.com> wrote:
>> On Sat, Dec 13, 2014 at 11:22 PM, Bjorn Andersson <bjorn@...o.se> wrote:
> [..]
>>> Or simply; what is vmmc (in the code) supposed to represent?
>>
>> Hi Bjorn,
>>
>> VMMC is the supply that delivers power out to the SD card itself (aka VDD).
>>
>> It is not the internal power rail/power domain of the host controller
>> within the SoC.
>>
>
> Thanks for you answer Tim, I'll write up a patch for the Qualcomm
> driver that add the possibility of specifying an internal supply for
> the devices where that uses that.
>
> My only concern is that for any standard compliant sdhci driver we're
> supposed to have a info printout that vmmc was not found (but vqmmc is
> there). But I guess that's a matter of proper documentation and hoping
> people don't pay too much attention to it?
>

Sorry, this is wrong.

We are routing the regulators straight to vdd of the memory and should
hence use vmmc to specify this. However unless I actually program 0x29
in the Qualcomm sdhci block I get no responses from the card.

Which I believe is correct behavior as the SDHC specification [1] says
the following about BIT(0) of 0x29:

"If this bit is cleared, the Host Controller shall immediately stop
driving CMD and DAT[3:0] (tri-state) and drive SDCLK to low level".


So I think 52221610d is indeed incorrect.

[1] https://www.sdcard.org/downloads/pls/simplified_specs/archive/partA2_300.pdf

Regards,
Bjorn
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