+Alex
On 1/11/2022 09:52, Rafael J. Wysocki wrote:
On Wed, Jan 5, 2022 at 8:39 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
Currently the Linux kernel will offer s2idle regardless of whether the FADT
indicates the system should use or on X86 if the LPS0 ACPI device has been
activated.
On some non-AMD platforms s2idle can be offered even without proper
firmware support. The power consumption may be higher in these instances
but the system otherwise properly suspends and resumes.
Well, the idea is that s2idle should not require FW support at all. >
May I ask - why? It's an intentional design decision?
It may not be possible to reach the minimum power level of the
platform without FW support, but that should not prevent s2idle from
being used.
On AMD platforms however when the FW has been configured not to offer
s2idle some different hardware initialization has occurred such that the
system won't properly resume.
That's rather unfortunate.
Can you please share some details on what's going on in those cases?
Technically, without FW support there should be no difference between
the platform state reachable via s2idle and the platform state
reachable via runtime idle.
During resume there is a number of page faults that occur and during
initialization the ring tests fail. The graphics is unusable at this
time as a result.
The amdgpu code actually *does* distinguish between the 3 different
cases of S3, S0ix, and runtime suspend.
The function "amdgpu_acpi_is_s0ix_active" causes different codepaths to
be used during the suspend routine.
In this particular case that FADT doesn't set the low power idle bit
and that function returns false meaning the s3 codepath is taken but
the hardware didn't go through a reset.
It *might* also be possible to solve this by mandating an ASIC reset in
such a case (we didn't try).
However it comes back to my first upleveveled question - is this a case
we really want to support and encourage? This type of bug and
combination of codepaths is not a case that is going to be well tested.
This patch series will align the kernel behavior to only what AMD validates.
