Re: [PATCH v2 11/15] PCI: rcar-gen4: Recover the Root Port on link down

[Marek Vasut]

On 9/28/26 6:52 PM, Koichiro Den wrote:
> On R-Car, the controller's reset requests (smlh_req_rst_not,
> link_req_rst_not) arrive on intreq_pcim_sub, the interrupt the MSIs are
> demultiplexed from, so DBI is read as soon as the link goes down. On
> R-Car S4 that is a hazard: DBI accesses issued within a few hundred
> microseconds of an unexpected link down do not complete and hang the
> host. In testing, the first Root Port config read after powering off
> the link partner hung unless delayed by ~300 us.
>
> Check the APP reset status in the interrupt handler before DBI is
> touched. When a reset request is latched, flag the controller as
> needing reinitialization, which masks the sources, ack the request and
> schedule recovery work. The work calls pci_host_handle_link_down() on
> the Root Port, which runs the AER-style recovery and resets the
> controller through reset_root_port(); it holds a reference on the port,
> which can be removed through sysfs meanwhile. The check also reports a
> recovery already pending, whether started by another interrupt or left
> over from a failed reset, so the handler issues no further DBI accesses
> until a reset succeeds.
>
> Arm the detection once enumeration is done, as the recovery needs the
> Root Port to exist. Only unmasked status bits are handled and pending
> latches are cleared when the sources are re-enabled, so requests
> recorded during probe or the reset itself do not trigger another
> recovery. Teardown only disarms the detection: MSI delivery has to keep
> working while devices are removed.
>
> Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>

Reviewed-by: Marek Vasut <marek.vasut+renesas@xxxxxxxxxxx>