linux-kernel - Re: [PATCH] qcom: sdhci-msm: enable the DLL clock

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Message-ID: <CAPDyKFp4Njdb7g6p_yM7E4MSqYiHGA4O1rB3wLy8X_F3q5j5nA@mail.gmail.com>
Date:	Wed, 13 Apr 2016 13:40:12 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Sreedhar Sambangi <ssambang@...eaurora.org>,
	Andy Gross <andy.gross@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	qca-upstream.external@....qualcomm.com,
	Ivan Ivanov <ivan.ivanov@...aro.org>,
	Georgi Djakov <georgi.djakov@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] qcom: sdhci-msm: enable the DLL clock

On 12 April 2016 at 00:11, Stephen Boyd <sboyd@...eaurora.org> wrote:
> On 04/11, Ulf Hansson wrote:
>> + Adrian
>>
>> On 5 April 2016 at 09:46, Sreedhar Sambangi <ssambang@...eaurora.org> wrote:
>> > The DLL clock has to be enabled until the correct
>> > clock frequency is delivered to DLL
>> > '1'(default) - DLL clock is disabled
>> > '0' - dll clock has legacly clock enable.
>> >
>> > Signed-off-by: Varadarajan Narayanan <varada@...eaurora.org>
>> > Signed-off-by: Sreedhar Sambangi <ssambang@...eaurora.org>
>>
>> Adrian Hunter is the maintainer for sdhci, next time make sure to post to him.
>>
>> As this seems like fairly trivial change I decided to pick it up
>> anyway. So applied for next!
>>
>> Note, that I changed the prefix of the commit message header to "mmc".
>>
>
> I'm not sure this patch is actually right. In the downstream
> sources we do quite a few more reads and writes if we need to
> poke this second DLL configuration register. Furthermore, on
> msm8974 and apq8084 this register doesn't even exist so writing
> to it may cause problems if it isn't write ignored (I haven't
> checked).
>
> I think we should follow the downstream kernel design instead.
> Namely, reading the major/minor version registers to figure out
> if we should be touching this register in the first place, and
> then adding a clock property to the DT binding for the XO source
> so we can determine the XO frequency. It seems that we need this
> frequency to figure out how to program the second DLL
> configuration register appropriately.

Stephen,

Thanks for reviewing. I have dropped this patch for now.

Kind regards
Uffe