linux-kernel - Re: [PATCH 2/2] mmc: sdhci-msm: Re-initialize DLL if MCLK is gated dynamically

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Date:   Thu, 27 Sep 2018 16:29:50 +0530
From:   Veerabhadrarao Badiganti <vbadigan@...eaurora.org>
To:     Doug Anderson <dianders@...gle.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Asutosh Das <asutoshd@...eaurora.org>, riteshh@...eaurora.org,
        stummala@...eaurora.org, sayalil@...eaurora.org,
        Evan Green <evgreen@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mmc: sdhci-msm: Re-initialize DLL if MCLK is gated
 dynamically

Hi Doug,


On 9/26/2018 3:58 AM, Doug Anderson wrote:
> Hi,
>
> On Tue, Sep 25, 2018 at 8:05 AM Veerabhadrarao Badiganti
> <vbadigan@...eaurora.org> wrote:
>> +       /*
>> +        * Whenever core-clock is gated dynamically, it's needed to
>> +        * re-initialize the DLL when the clock is ungated.
>> +        */
>> +       if (msm_host->restore_dll_cfg_needed && msm_host->clk_rate) {
>> +               msm_host->restore_dll_cfg = true;
>> +               mmc_retune_needed(host->mmc);
> Using the boolean "restore_dll_cfg" to communicate like this seems
> really fragile.  I have no basis in fact, but I worry that something
> will happen in the meantime that really ought to invalidate the
> "saved_tuning_phase" but the boolean will still be set.
>
> Is there a reason you can't just call msm_config_cm_dll_phase()
> directly from sdhci_msm_runtime_resume()?  Perhaps after the
> clk_bulk_prepare_enable() call below?

I can do that.

But we don't need to restore the clock phase for all speed modes since 
every mode
doesn't use DLL. Only few speed modes (only SDR104 mode for SD card)
would need to restore DLL setting. So I would need to do some extra checks
for performing this operation for only required speed modes.
And we should re-initialize the DLL first before programming the phase.

I wanted to reuse the existing logic which does all these things. So did 
this way.

>
> -Doug
Thanks
Veera