Re: [PATCH v4 02/12] PCI: aardvark: Don't blindly enable ASPM L0s and don't write to read-only register

Rob Herring
2020-05-07T21:07:17Z

On Thu, 30 Apr 2020 10:06:15 +0200, =?UTF-8?q?Pali=20Roh=C3=A1r?= wrote:
> Trying to change Link Status register does not have any effect as this
> is a read-only register. Trying to overwrite bits for Negotiated Link
> Width does not make sense.
>
> In future proper change of link width can be done via Lane Count Select
> bits in PCIe Control 0 register.
>
> Trying to unconditionally enable ASPM L0s via ASPM Control bits in Link
> Control register is wrong. There should be at least some detection if
> endpoint supports L0s as isn't mandatory.
>
> Moreover ASPM Control bits in Link Control register are controlled by
> pcie/aspm.c code which sets it according to system ASPM settings,
> immediately after aardvark driver probes. So setting these bits by
> aardvark driver has no long running effect.
>
> Remove code which touches ASPM L0s bits from this driver and let
> kernel's ASPM implementation to set ASPM state properly.
>
> Some users are reporting issues that this code is problematic for some
> Intel wifi cards and removing it fixes them, see e.g.:
> https://bugzilla.kernel.org/show_bug.cgi?id=196339
>
> If problems with Intel wifi cards occur even after this commit, then
> pcie/aspm.c code could be modified / hooked to not enable ASPM L0s state
> for affected problematic cards.
>
> Signed-off-by: Pali Rohár <pali@kernel.org>
> ---
> drivers/pci/controller/pci-aardvark.c | 4 ----
> 1 file changed, 4 deletions(-)
>

Acked-by: Rob Herring <robh@kernel.org>