linux-kernel - Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated

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Date:   Wed, 30 Jun 2021 21:59:58 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Robinson <pbrobinson@...il.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Michal Simek <michal.simek@...inx.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with
 clocks gated

On 6/30/21 8:59 PM, Bjorn Helgaas wrote:
> [+cc Michal, Jingoo, Thierry, Jonathan]

[snip]

> 
> I think the above commit log is perfectly accurate, but all the
> details might suggest that this is something specific to rockchip or
> CONFIG_DEBUG_SHIRQ, which it isn't, and they might obscure the
> fundamental problem, which is actually very simple: we registered IRQ
> handlers before we were ready for them to be called.
> 
> I propose the following commit log in the hope that it would help
> other driver authors to make similar fixes:
>
>     PCI: rockchip: Register IRQ handlers after device and data are ready
> 
>     An IRQ handler may be called at any time after it is registered, so
>     anything it relies on must be ready before registration.
> 
>     rockchip_pcie_subsys_irq_handler() and rockchip_pcie_client_irq_handler()
>     read registers in the PCIe controller, but we registered them before
>     turning on clocks to the controller.  If either is called before the clocks
>     are turned on, the register reads fail and the machine hangs.
> 
>     Similarly, rockchip_pcie_legacy_int_handler() uses rockchip->irq_domain,
>     but we installed it before initializing irq_domain.
> 
>     Register IRQ handlers after their data structures are initialized and
>     clocks are enabled.
> 
> If this is inaccurate or omits something important, let me know.  I
> can make any updates locally.
>

I think your description is accurate and agree that the commit message may
be misleading. As you said, this is a general problem and the fact that an
IRQ is shared and CONFIG_DEBUG_SHIRQ fires a spurious interrupt just make
the assumptions in the driver to fall apart.

But maybe you can also add a paragraph that mentions the CONFIG_DEBUG_SHIRQ
option and shared interrupts? That way, other driver authors could know that
by enabling this an underlying problem might be exposed for them to fix.

Best regards,
-- 
Javier Martinez Canillas
Software Engineer
New Platform Technologies Enablement team
RHEL Engineering