linux-kernel - Re: [PATCH 8/9] ata: Add support for the Tegra124 SATA controller

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Message-ID: <53A07CED.7010503@wwwdotorg.org>
Date:	Tue, 17 Jun 2014 11:37:49 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mikko Perttunen <mikko.perttunen@...si.fi>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
CC:	Mikko Perttunen <mperttunen@...dia.com>, thierry.reding@...il.com,
	tj@...nel.org, pdeschrijver@...dia.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH 8/9] ata: Add support for the Tegra124 SATA controller

On 06/17/2014 11:36 AM, Mikko Perttunen wrote:
> On 06/17/2014 08:04 PM, Bartlomiej Zolnierkiewicz wrote:
>>
>> Hi,
>>
>> On Tuesday, June 17, 2014 10:10:23 AM Stephen Warren wrote:
>>> On 06/17/2014 06:14 AM, Bartlomiej Zolnierkiewicz wrote:
>>
>> [...]
>>
>>>>> +static struct platform_driver tegra_ahci_driver = {
>>>>> +    .probe = tegra_ahci_probe,
>>>>> +    .remove = ata_platform_remove_one,
>>>>> +    .driver = {
>>>>> +        .name = "tegra-ahci",
>>>>> +        .owner = THIS_MODULE,
>>>>> +        .of_match_table = tegra_ahci_of_match,
>>>>> +    },
>>>>
>>>> This driver lacks PM suspend/resume support.  I assume that
>>>> the Tegra124 platform also doesn't support suspend/resume yet
>>>> (if so a comment in the driver code about this would be useful),
>>>> otherwise the driver should be fixed.
>>>
>>> We do have basic system suspend/resume support. However, I don't think
>>> missing suspend/resume in an individual driver should stop it from being
>>> merged. It can certainly be added later.
>>
>> There should be at least FIXME in the driver explaining the situation and
>> I would really prefer to have PM support added when the driver is still
>> "hot" (meaning there are people actively working on it) instead of
>> possibly
>> having to chase people months/years later when they have already moved on
>> and are working on something else.  Please also note that adding PM
>> support
>> should be quite simple if the driver is designed correctly.
>
> AFAIK, the deepest level of suspend currently supported on upstream is
> LP1, for which the driver doesn't need to do anything. Only when we go
> to LP0 the driver will need to save/reload registers and stuff.

Yes, it's generally true that no SoC register state is lost during
suspend, only CPU state.
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