linux-kernel - Re: [PATCH v2 3/3] ata: ahci: Skip 200 ms debounce delay for AMD 300 Series Chipset SATA Controller

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Message-ID: <3135eed0-b7e3-42fa-5b6c-80360f34e428@opensource.wdc.com>
Date:   Wed, 1 Jun 2022 17:58:35 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Mario Limonciello <Mario.Limonciello@....com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] ata: ahci: Skip 200 ms debounce delay for AMD 300
 Series Chipset SATA Controller

On 6/1/22 01:18, Paul Menzel wrote:
>>>> With that in mind, I am not planning to apply your previous patches
>>>> for 5.18, as they would conflict and would only end up being churn
>>>> since the delay removal by default will undo your changes.
>>> Obviously, I do not agree, as this would give the a little bit more
>>> testing already, if changing the default is a good idea. Also, if the
>>> conflict will be hard to resolve, I happily do it (the patches could
>>> even be reverted on top – git commits are cheap and easy to handle).
>>
>> The conflict is not hard to resolve. The point is that my patches changing
>> the default to no debounce delay completely remove the changes of your
>> patch to do the same for one or some adapters. So adding your patches now
>> and then my patches on top does not make much sense at all.
>>
>> If too many problems show up and I end up reverting/removing the patches,
>> then I will be happy to take your patches for the adapter you tested. Note
>> that *all* the machines I have tested so far are OK without a debounce
>> delay too. So we could add them too... And endup with a long list of
>> adapters that use the default ahci driver without debounce delay. The goal
>> of changing the default to no delay is to avoid that. So far, the adapters
>> I have identified that need the delay have their own declaration, so we
>> only need to add a flag there. Simpler change that listing up adapters
>> that are OK without the delay.
>>
>>> Anyway, I wrote my piece, but you are the maintainer, so it’s your call
>>> and I stop bothering you.
> 
> I just wanted to inquire about the status of your changes? I do not find 
> them in your `for-5.19` branch. As they should be tested in linux-next 
> before the merge window opens, if these are not ready yet, could you 
> please apply my (tested) patches?

I could, but 5.19 now has an updated libata.force kernel parameter that
allows one to disable the debounce delay for a particular port or for all
ports of an adapter. See libata.force=x.y:nodbdelay for a port y of
adapter x or libata.force=x:nodbdelay for all ports of adapter x.

I still plan to revisit the arbitrary link debounce timers but I prefer to
have the power management cleanup applied first. The reason is that link
debounce depends on PHY readiness, which itself depends heavily on power
mode transitions. My plan is to get this done during this cycle for
release with 5.20 and then fix on top the arbitrary delays for 5.21.

Is the libata.force solution OK for you until we have a final more solid
fix that can benefit most modern adapters (and not just the ones you
identified) ? If you do have a use case that needs a "nodbdelay" horkage
due to some constraint in the field, then I will apply your patches, but
they likely will be voided by coming changes. Let me know.

Cheers.


-- 
Damien Le Moal
Western Digital Research