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

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Message-ID: <YUh6r6SOu7AH6P3f@sashalap>
Date:   Mon, 20 Sep 2021 08:12:31 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Marek Vasut <marek.vasut@...il.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        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 Sat, Sep 11, 2021 at 06:05:37PM +0200, Marek Vasut wrote:
>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/

I see that it's not upstream yet, so I'll drop this patch for now.

-- 
Thanks,
Sasha