linux-kernel - Re: [PATCH v6 0/4] PCI: Add support for resetting the Root Ports in a platform specific way

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Message-ID: <zhu77qldhrr7ovp2g2tpusl67zsacjx5oapnaasxo2ybmhfohn@io3oqqc6gtte>
Date: Fri, 29 Aug 2025 19:26:56 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Brian Norris <briannorris@...omium.org>
Cc: manivannan.sadhasivam@....qualcomm.com, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, 
	Oliver O'Halloran <oohall@...il.com>, Will Deacon <will@...nel.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Rob Herring <robh@...nel.org>, Heiko Stuebner <heiko@...ech.de>, 
	Philipp Zabel <p.zabel@...gutronix.de>, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org, 
	linux-arm-msm@...r.kernel.org, linux-rockchip@...ts.infradead.org, 
	Niklas Cassel <cassel@...nel.org>, Wilfred Mallawa <wilfred.mallawa@....com>, 
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH v6 0/4] PCI: Add support for resetting the Root Ports in
 a platform specific way

On Thu, Aug 28, 2025 at 01:01:51PM GMT, Brian Norris wrote:
> On Tue, Jul 15, 2025 at 07:51:03PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > Hi,
> > 
> > Currently, in the event of AER/DPC, PCI core will try to reset the slot (Root
> > Port) and its subordinate devices by invoking bridge control reset and FLR. But
> > in some cases like AER Fatal error, it might be necessary to reset the Root
> > Ports using the PCI host bridge drivers in a platform specific way (as indicated
> > by the TODO in the pcie_do_recovery() function in drivers/pci/pcie/err.c).
> > Otherwise, the PCI link won't be recovered successfully.
> > 
> > So this series adds a new callback 'pci_host_bridge::reset_root_port' for the
> > host bridge drivers to reset the Root Port when a fatal error happens.
> > 
> > Also, this series allows the host bridge drivers to handle PCI link down event
> > by resetting the Root Ports and recovering the bus. This is accomplished by the
> > help of the new 'pci_host_handle_link_down()' API. Host bridge drivers are
> > expected to call this API (preferrably from a threaded IRQ handler) with
> > relevant Root Port 'pci_dev' when a link down event is detected for the port.
> > The API will reuse the pcie_do_recovery() function to recover the link if AER
> > support is enabled, otherwise it will directly call the reset_root_port()
> > callback of the host bridge driver (if exists).
> > 
> > For reference, I've modified the pcie-qcom driver to call
> > pci_host_handle_link_down() API with Root Port 'pci_dev' after receiving the
> > LINK_DOWN global_irq event and populated 'pci_host_bridge::reset_root_port()'
> > callback to reset the Root Port. Since the Qcom PCIe controllers support only
> > a single Root Port (slot) per controller instance, the API is going to be
> > invoked only once. For multi Root Port controllers, the controller driver is
> > expected to detect the Root Port that received the link down event and call
> > the pci_host_handle_link_down() API with 'pci_dev' of that Root Port.
> > 
> > Testing
> > -------
> > 
> > I've lost access to my test setup now. So Krishna (Cced) will help with testing
> > on the Qcom platform and Wilfred or Niklas should be able to test it on Rockchip
> > platform. For the moment, this series is compile tested only.
> 
> For the series:
> 
> Tested-by: Brian Norris <briannorris@...omium.org>
> 
> I've tested the whole thing on Qualcomm SC7280 Herobrine systems with
> NVMe. After adding a debugfs node to control toggling PERST, I can force
> the link to reset, and see it recover and resume NVMe traffic.
> 
> I've tested the first two on Pixel phones, using a non-upstream
> DWC-based driver that I'm working on getting in better shape. (We've
> previously supported a custom link-error API setup instead.) I'd love to
> see this available upstream.
> 

Thanks, Brian for testing! I didn't get time to look into the report from
Niklas (which is the only blocking thing for this series). I'll try to dig into
it today/tomorrow.

- Mani

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