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

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Date:   Thu, 7 May 2020 16:07:13 -0500
From:   Rob Herring <robh@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     Jason Cooper <jason@...edaemon.net>, Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Remi Pommarel <repk@...plefau.lt>,
        Marek Behún <marek.behun@....cz>,
        Tomasz Maciej Nowak <tmn505@...il.com>,
        Xogium <contact@...ium.me>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v4 02/12] PCI: aardvark: Don't blindly enable ASPM L0s
 and don't write to read-only register

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@...nel.org>
> ---
>  drivers/pci/controller/pci-aardvark.c | 4 ----
>  1 file changed, 4 deletions(-)
> 

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