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

From: Bjorn Helgaas <helgaas@kernel.org>
To: Javier Martinez Canillas <javierm@redhat.com>
Cc: linux-kernel@vger.kernel.org,
	Peter Robinson <pbrobinson@gmail.com>,
	Shawn Lin <shawn.lin@rock-chips.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Rob Herring <robh@kernel.org>,
	linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org,
	linux-rockchip@lists.infradead.org
Subject: Re: [PATCH v2] PCI: rockchip: Avoid accessing PCIe registers with clocks gated
Date: Thu, 24 Jun 2021 16:57:50 -0500	[thread overview]
Message-ID: <20210624215750.GA3556174@bjorn-Precision-5520> (raw)
In-Reply-To: <20210608080409.1729276-1-javierm@redhat.com>

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.

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