linux-kernel - Re: [PATCH v3] PCI: aardvark: Use LTSSM state to build link training flag

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Message-ID: <20190925143200.696af4cf@windsurf>
Date:   Wed, 25 Sep 2019 14:32:00 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...tlin.com>
To:     Remi Pommarel <repk@...plefau.lt>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ellie Reeves <ellierevves@...il.com>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PCI: aardvark: Use LTSSM state to build link
 training flag

Hello Remi,

On Wed, 22 May 2019 23:33:51 +0200
Remi Pommarel <repk@...plefau.lt> wrote:

> Aardvark's PCI_EXP_LNKSTA_LT flag in its link status register is not
> implemented and does not reflect the actual link training state (the
> flag is always set to 0). In order to support link re-training feature
> this flag has to be emulated. The Link Training and Status State
> Machine (LTSSM) flag in Aardvark LMI config register could be used as
> a link training indicator. Indeed if the LTSSM is in L0 or upper state
> then link training has completed (see [1]).
> 
> Unfortunately because after asking a link retraining it takes a while
> for the LTSSM state to become less than 0x10 (due to L0s to recovery
> state transition delays), LTSSM can still be in L0 while link training
> has not finished yet. So this waits for link to be in recovery or lesser
> state before returning after asking for a link retrain.
> 
> [1] "PCI Express Base Specification", REV. 4.0
>     PCI Express, February 19 2014, Table 4-14
> 
> Signed-off-by: Remi Pommarel <repk@...plefau.lt>

Here as well, sorry for the very long delay, and many thanks for the
great research work, including the arm-trusted-firmware fix. I reviewed
the implementation, and tested on my Armada 3720 DB board with a E1000E
NIC, and it all looks good to me.

Acked-by: Thomas Petazzoni <thomas.petazzoni@...tlin.com>

Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com