linux-kernel - Re: [PATCH AUTOSEL 5.14 12/32] PCI: rcar: Add L1 link state fix into data abort hook

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Date:   Sat, 11 Sep 2021 18:05:37 +0200
From:   Marek Vasut <marek.vasut@...il.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Marek Vasut <marek.vasut+renesas@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Wolfram Sang <wsa@...-dreams.de>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        linux-renesas-soc@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.14 12/32] PCI: rcar: Add L1 link state fix into
 data abort hook

On 9/11/21 3:11 PM, Sasha Levin wrote:
> From: Marek Vasut <marek.vasut+renesas@...il.com>
> 
> [ Upstream commit a115b1bd3af0c2963e72f6e47143724c59251be6 ]
> 
> When the link is in L1, hardware should return it to L0
> automatically whenever a transaction targets a component on the
> other end of the link (PCIe r5.0, sec 5.2).
> 
> The R-Car PCIe controller doesn't handle this transition correctly.
> If the link is not in L0, an MMIO transaction targeting a downstream
> device fails, and the controller reports an ARM imprecise external
> abort.
> 
> Work around this by hooking the abort handler so the driver can
> detect this situation and help the hardware complete the link state
> transition.
> 
> When the R-Car controller receives a PM_ENTER_L1 DLLP from the
> downstream component, it sets PMEL1RX bit in PMSR register, but then
> the controller enters some sort of in-between state.  A subsequent
> MMIO transaction will fail, resulting in the external abort.  The
> abort handler detects this condition and completes the link state
> transition by setting the L1IATN bit in PMCTLR and waiting for the
> link state transition to complete.

You will also need the following patch, otherwise the build will fail on 
configurations without COMMON_CLK (none where this driver is used, but 
happened on one of the build bots). I'm waiting for PCIe maintainers to 
pick it up:
https://patchwork.kernel.org/project/linux-pci/patch/20210907144512.5238-1-marek.vasut@gmail.com/