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

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Date:   Thu, 22 Sep 2016 20:02:41 +0530
From:   Ritesh Harjani <riteshh@...eaurora.org>
To:     Pramod Gurav <pramod.gurav@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     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

Hi Pramod,

On 9/15/2016 7:28 PM, Pramod Gurav wrote:
> On 15 September 2016 at 15:49, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 15 September 2016 at 09:59, Pramod Gurav <pramod.gurav@...aro.org> wrote:
>>> On 9 September 2016 at 15:48, Georgi Djakov <georgi.djakov@...aro.org> wrote:
>>>> On 09/08/2016 11:02 AM, Adrian Hunter wrote:
>>>>>
>>>>> On 01/09/16 17:23, Pramod Gurav wrote:
>>>>>>
>>>>>> Provides runtime PM callbacks to enable and disable clock resources
>>>>>> when idle. Also support system PM callbacks to be called during system
>>>>>> suspend and resume.
>>>>>>
>>>>>> Signed-off-by: Pramod Gurav <pramod.gurav@...aro.org>
>>>>>
>>>>>
>>>>> Can we get some Tested/Reviewed/Acked-by from people using this driver?
>>>>>
>>>>
>>>> Hi Pramod,
>>>> Thanks for the patch. Unfortunately, my db410c board fails to
>>>> boot when i apply it.
>>>>
>>>
>>> Thanks Georgi for testing the patch. Its my wrong I did not update my
>>> kernel and continued fixing comments on old kernel.
>>> After spending some time I came to know that below change is causing the issue:
>>>
>>> Author: Dong Aisheng <aisheng.dong@....com>
>>> Date:   Tue Jul 12 15:46:17 2016 +0800
>>>
>>>     mmc: sdhci: add standard hw auto retuning support
>>>
>>>     If HW supports SDHCI_TUNING_MODE_3 which is auto retuning, we won't
>>>     retune during runtime suspend and resume, instead we use Re-tuning
>>>     Request signaled via SDHCI_INT_RETUNE interrupt to do retuning and
>>>     hw auto retuning during data transfer to guarantee the signal sample
>>>     window correction.
>>>
>>>     This can avoid a mass of repeatedly retuning during small file system
>>>     data access and improve the performance.
>>>
>>> Specially these lines that was added to suspend path:
>>>
>>> +       if (host->tuning_mode != SDHCI_TUNING_MODE_3)
>>> +               mmc_retune_needed(host->mmc);
>>>
>>> During sdhci setup in msm driver, the host returns the values to set
>>> sdhci auto tuning as supported.
>>> Hence host->tuning_mode is set to SDHCI_TUNING_MODE_3 during setup.
>>> But some how the auto tuning is not happening.
>>> Just to verify my case, I removed the 'if' part in above code and got
>>> the FS mounted.
>>>
>>> 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.


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
>