linux-kernel - Re: [PATCH v4 04/12] PCI: aardvark: Improve link training

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Message-ID: <20200507211015.GA31477@bogus>
Date:   Thu, 7 May 2020 16:10:15 -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 04/12] PCI: aardvark: Improve link training

On Thu, 30 Apr 2020 10:06:17 +0200, =?UTF-8?q?Pali=20Roh=C3=A1r?= wrote:
> From: Marek Behún <marek.behun@....cz>
> 
> Currently the aardvark driver trains link in PCIe gen2 mode. This may
> cause some buggy gen1 cards (such as Compex WLE900VX) to be unstable or
> even not detected. Moreover when ASPM code tries to retrain link second
> time, these cards may stop responding and link goes down. If gen1 is
> used this does not happen.
> 
> Unconditionally forcing gen1 is not a good solution since it may have
> performance impact on gen2 cards.
> 
> To overcome this, read 'max-link-speed' property (as defined in PCI
> device tree bindings) and use this as max gen mode. Then iteratively try
> link training at this mode or lower until successful. After successful
> link training choose final controller gen based on Negotiated Link Speed
> from Link Status register, which should match card speed.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> Signed-off-by: Marek Behún <marek.behun@....cz>
> ---
>  drivers/pci/controller/pci-aardvark.c | 114 ++++++++++++++++++++------
>  1 file changed, 89 insertions(+), 25 deletions(-)
> 

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