linux-kernel - Re: [PATCH v4 4/5] PCI: host-common: Add link down handling for host bridges

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Message-ID: <dglc4iqxxrjnbpqazi2xuzdblpcszcdb7q5nlz2ezzzyeujpvc@672myo6djcji>
Date: Wed, 14 May 2025 17:33:15 +0100
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Mahesh J Salgaonkar <mahesh@...ux.ibm.com>, 
	Oliver O'Halloran <oohall@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Zhou Wang <wangzhou1@...ilicon.com>, 
	Will Deacon <will@...nel.org>, Robert Richter <rric@...nel.org>, 
	Alyssa Rosenzweig <alyssa@...enzweig.io>, Marc Zyngier <maz@...nel.org>, 
	Conor Dooley <conor.dooley@...rochip.com>, Daire McNamara <daire.mcnamara@...rochip.com>, 
	dingwei@...vell.com, cassel@...nel.org, Lukas Wunner <lukas@...ner.de>, 
	linuxppc-dev@...ts.ozlabs.org, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 4/5] PCI: host-common: Add link down handling for host
 bridges

On Wed, May 14, 2025 at 12:00:11PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 5/8/2025 12:40 PM, Manivannan Sadhasivam wrote:
> > The PCI link, when down, needs to be recovered to bring it back. But that
> > cannot be done in a generic way as link recovery procedure is specific to
> > host bridges. So add a new API pci_host_handle_link_down() that could be
> > called by the host bridge drivers when the link goes down.
> > 
> > The API will iterate through all the slots and calls the pcie_do_recovery()
> > function with 'pci_channel_io_frozen' as the state. This will result in the
> > execution of the AER Fatal error handling code. Since the link down
> > recovery is pretty much the same as AER Fatal error handling,
> > pcie_do_recovery() helper is reused here. First the AER error_detected
> > callback will be triggered for the bridge and the downstream devices. Then,
> > pci_host_reset_slot() will be called for the slot, which will reset the
> > slot using 'reset_slot' callback to recover the link. Once that's done,
> > resume message will be broadcasted to the bridge and the downstream devices
> > indicating successful link recovery.
> > 
> > In case if the AER support is not enabled in the kernel, only
> > pci_bus_error_reset() will be called for each slots as there is no way we
> > could inform the drivers about link recovery.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >   drivers/pci/controller/pci-host-common.c | 58 ++++++++++++++++++++++++++++++++
> >   drivers/pci/controller/pci-host-common.h |  1 +
> >   drivers/pci/pci.c                        |  1 +
> >   drivers/pci/pcie/err.c                   |  1 +
> >   4 files changed, 61 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> > index f93bc7034e697250711833a5151f7ef177cd62a0..f916f0a874a61ddfbfd99f96975c00fb66dd224c 100644
> > --- a/drivers/pci/controller/pci-host-common.c
> > +++ b/drivers/pci/controller/pci-host-common.c
> > @@ -12,9 +12,11 @@
> >   #include <linux/of.h>
> >   #include <linux/of_address.h>
> >   #include <linux/of_pci.h>
> > +#include <linux/pci.h>
> >   #include <linux/pci-ecam.h>
> >   #include <linux/platform_device.h>
> > +#include "../pci.h"
> >   #include "pci-host-common.h"
> >   static void gen_pci_unmap_cfg(void *ptr)
> > @@ -96,5 +98,61 @@ void pci_host_common_remove(struct platform_device *pdev)
> >   }
> >   EXPORT_SYMBOL_GPL(pci_host_common_remove);
> > +#if IS_ENABLED(CONFIG_PCIEAER)
> > +static pci_ers_result_t pci_host_reset_slot(struct pci_dev *dev)
> > +{
> > +	int ret;
> > +
> > +	ret = pci_bus_error_reset(dev);
> > +	if (ret) {
> > +		pci_err(dev, "Failed to reset slot: %d\n", ret);
> > +		return PCI_ERS_RESULT_DISCONNECT;
> > +	}
> > +
> > +	pci_info(dev, "Slot has been reset\n");
> > +
> > +	return PCI_ERS_RESULT_RECOVERED;
> > +}
> > +
> > +static void pci_host_recover_slots(struct pci_host_bridge *host)
> > +{
> > +	struct pci_bus *bus = host->bus;
> > +	struct pci_dev *dev;
> > +
> > +	for_each_pci_bridge(dev, bus) {
> > +		if (!pci_is_root_bus(bus))
> bus here is always constant here, we may need to have check
> for dev here like if (!pci_is_root_bus(dev->bus))

Good catch! Ammended it while applying.

- Mani

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