linux-kernel - Re: [PATCH v4 3/3] ata: ahci_tegra: Add AHCI support for Tegra186

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Message-ID: <2ef2a124-9e4b-bc02-3830-8ef077638ced@gmail.com>
Date:   Thu, 8 Apr 2021 02:25:19 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>, axboe@...nel.dk,
        thierry.reding@...il.com, jonathanh@...dia.com, robh+dt@...nel.org
Cc:     pchandru@...dia.com, devicetree@...r.kernel.org,
        linux-ide@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] ata: ahci_tegra: Add AHCI support for Tegra186

08.04.2021 02:00, Sowjanya Komatineni пишет:
> 
> On 4/7/21 3:57 PM, Sowjanya Komatineni wrote:
>>
>> On 4/7/21 2:36 PM, Dmitry Osipenko wrote:
>>> 07.04.2021 04:25, Sowjanya Komatineni пишет:
>>>> +    if (!tegra->pdev->dev.pm_domain) {
>>>> +        ret = tegra_powergate_sequence_power_up(TEGRA_POWERGATE_SATA,
>>>> +                            tegra->sata_clk,
>>>> +                            tegra->sata_rst);
>>>> +        if (ret)
>>>> +            goto disable_regulators;
>>>> +    }
>>> Hi,
>>>
>>> Why you haven't added condition for tegra_powergate_power_off()? I think
>>> it should break GENPD and legacy PD API isn't not supported by T186
>>> at all.
>>>
>>> I'm also not sure whether the power up/down sequence is correct using
>>> GENPD.
>>>
>>> Moreover the driver doesn't support runtime PM, so GENPD should be
>>> always off?
>>
>> This driver already using legacy PD API's so thought its supported and
>> added power domain device check during powergate_sequence_power_up and
>> yes same should apply for powergate_power_off as well. But if legacy
>> PD is not supported by T186 then not sure why original driver even
>> using these API's.
>>
>>
> Sorry just took a look and driver supports T210 and prior tegra as well.
> T210 and prior supports legacy PD and this check is applicable for
> those. So we should add power domain device check for power off as well.

You could fix it with a follow up patch. Please try to test that
power-off works properly, at least try to unload the driver module and
re-load it.

> But for T186, we should have GENPD working once we add runtime PM
> support to driver.
> 
> Preetham/Thierry, Can you confirm where SATA is un powergated prior to
> kernel?
> 
> 
>> But as RPM is not implemented yet for this driver, GENPD will be OFF
>> but SATA is not in power-gate by the time kernel starts and
>> functionally works.
>>
>> But with RPM implementation, I guess we can do proper power gate on/off.
>>

I now recalled that GENPD turns ON all domains by default and then turns
them OFF only when driver entered into the RPM-suspended state. This
means that AHCI GENPD should be always-ON for T186, which should be okay
if this doesn't break power sequences.