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

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Date:   Thu, 24 Jun 2021 16:57:50 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
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
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with
 clocks gated

On Tue, Jun 08, 2021 at 10:04:09AM +0200, Javier Martinez Canillas wrote:
> IRQ handlers that are registered for shared interrupts can be called at
> any time after have been registered using the request_irq() function.
> 
> It's up to drivers to ensure that's always safe for these to be called.
> 
> Both the "pcie-sys" and "pcie-client" interrupts are shared, but since
> their handlers are registered very early in the probe function, an error
> later can lead to these handlers being executed before all the required
> resources have been properly setup.
> 
> For example, the rockchip_pcie_read() function used by these IRQ handlers
> expects that some PCIe clocks will already be enabled, otherwise trying
> to access the PCIe registers causes the read to hang and never return.

The read *never* completes?  That might be a bit problematic because
it implies that we may not be able to recover from PCIe errors.  Most
controllers will timeout eventually, log an error, and either
fabricate some data (typically ~0) to complete the CPU's read or cause
some kind of abort or machine check.

Just asking in case there's some controller configuration that should
be tweaked.