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Message-ID: <ee9a51e2-1733-dcd5-7514-0b8d1c1fa430@redhat.com>
Date:   Fri, 25 Feb 2022 22:07:29 +0100
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Subject: Re: [PATCH v2 1/3] ata: ahci: Rename board_ahci_mobile
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To:     "Limonciello, Mario" <Mario.Limonciello@amd.com>,
        Christoph Hellwig <hch@infradead.org>
Cc:     Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "pmenzel@molgen.mpg.de" <pmenzel@molgen.mpg.de>
References: <20220225061113.223920-1-mario.limonciello@amd.com>
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From:   Hans de Goede <hdegoede@redhat.com>
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Hi,

On 2/25/22 17:19, Limonciello, Mario wrote:
> [Public]
> 
>> On 2/25/22 17:04, Limonciello, Mario wrote:
>>> [Public]
>>>
>>>> On Fri, Feb 25, 2022 at 12:11:11AM -0600, Mario Limonciello wrote:
>>>>> This board definition was originally created for mobile devices to
>>>>> designate default link power managmeent policy to influence runtime
>>>>> power consumption.
>>>>>
>>>>> As this is interesting for more than just mobile designs, rename the
>>>>> board to `board_ahci_low_power` to make it clear it is about default
>>>>> policy.
>>>>
>>>> Is there any good reason to not just apply the policy to all devices
>>>> by default?
>>>
>>> That sure would make this all cleaner.
>>>
>>> I think Hans knows more of the history here than anyone else.  I had
>>> presumed there was some data loss scenarios with some of the older
>>> chipsets.
>>
>> When I first introduced this change there were reports of crashes and
>> data corruption caused by setting the policy to min_power, these were
>> tied to some motherboards and/or to some drives.
>>
>> This is the whole reason why I only enabled this on a subset of all the
>> AHCI chipsets.
>>
>> At least on devices with a chipset which is currently marked as
>> mobile, the motherboard specific issues could be fixed with a BIOS
>> update. But I doubt that similar BIOS fixes have also been rolled
>> out to all desktop boards (and have been applied by all users),
>> and I also don't know about older boards.
>>
>> So enabling this on all chipsets is definitely not without risks.
>>
> 
> This was before min_power_with_partial and min_power_with_dipm
> were introduced though right?

The issues where some laptops needed BIOS updates was with fedora
using min_power_with_dipm as default for mobile chipsets.

>  Maybe another way to look at this
> is to drop the policy min_power, which overall is dangerous.

Maybe, see above. I'm not going to block this if people want
to give this a try, but it is going to require someone keeping
a very close look at any issues popping up and we must be
prepared to roll-back the change if necessary.

Regards,

Hans