linux-kernel - Re: [PATCH v3] mmc: sdhci-msm: Add pm

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Date:   Fri, 23 Sep 2016 12:07:37 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Ritesh Harjani <riteshh@...eaurora.org>
Cc:     Pramod Gurav <pramod.gurav@...aro.org>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v3] mmc: sdhci-msm: Add pm_runtime and system PM support

[...]

>>>> Is there anything else needed in msm sdhci driver so that the auto
>>>> tuning is taken care of?
>>>
>>>
>>> I am not familiar with any other than sdhci-esdhc-imx which supports
>>> the SDHCI_TUNING_MODE_3. I may be wrong though.
>>>
>>> In the sdhci-esdhc-imx case, enabling of auto tuning seems to be done
>>> in esdhc_post_tuning(), where a vendor specific register
>>> (ESDHC_MIX_CTRL) is being written to. Perhaps something similar in
>>> your case?
>>>
>> Thanks Ulf for the comments. Will check this and see if there is
>> something of this sort we have to do to achieve auto tuning.
>> Adding Ritesh who has been posting some SDHCI MSM patches recently in
>> case he knows about this.
>
>
> Internally, we don't use this Auto re-tuning and rely on explicit re-tune by
> host driver.
>
> Question though -
> 1. why do we need to call sdhci_runtime_resume/suspend from
> sdhci_msm_runtime_suspend/resume?
> From what I see is, sdhci_runtime_susend/resume will do reset and re-program
> of host->pwr and host->clk because of which a retune will be required for
> the next command after runtime resume.
>
> We can *only* disable and enable the clocks in
> sdhci_msm_runtime_suspend/resume?
> Thoughts? With this, I suppose you would not see any issue.

I see.

I assumes that means saving/restoring register context will
automatically handled by some other outer logic, when doing clock
gating/ungating?

In other words, if the controller has valid tuning values, those will
be re-used and restored when clock ungating happens?

>
>
> Though for this issue, since internally also auto retuning is never used, we
> can have this mode disabled. I can once again check with HW team to get more
> details about this mode for MSM controller.
>
>>
>> Regards,
>> Pramod
>>
>

Kind regards
Uffe