Re: [PATCH] PCI/sysfs: Protect driver's D3cold preference from user space

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On 9/18/2023 09:26, Lukas Wunner wrote:
On Mon, Sep 18, 2023 at 08:28:51AM -0500, Mario Limonciello wrote:
On 9/18/2023 08:24, Lukas Wunner wrote:
On Mon, Sep 18, 2023 at 08:14:21AM -0500, Mario Limonciello wrote:
What's the history behind why userspace is allowed to opt a device out of
D3cold in the first place?

It feels like it should have been a debugging only thing to me.

That's a fair question.

Apparently the default for d3cold_allowed was originally "false"
and user space could opt in to D3cold.  Then commit 4f9c1397e2e8
("PCI/PM: Enable D3/D3cold by default for most devices") changed
the default to "true".  That was 11 years ago.

I agree that today this should all work automatically and a
user space option to disable D3cold on a per-device basis only
really makes sense as a debugging aid, hence belongs in debugfs.

Thanks.  Then perhaps as part of moving it to debugfs it makes sense to
simplify the logic.

d3cold_allowed is documented in Documentation/ABI/testing/sysfs-bus-pci,
so it's user space ABI which we're not allowed to break.  We'd have to
declare it deprecated, emit a warning when it's used and slowly phase
it out over the years.

What about as part of deprecating it to make it always return -EINVAL no matter the input? The ABI isn't broken, but it allows for the optimization.

Until then, the $SUBJECT_PATCH probably still makes sense to reinstate
the behavior we had until 2016...



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