Re: [PATCH 07/11] PCI: rcar-gen4: Recover the Root Port on link down

[Marek Vasut <marek.vasut@mailbox.org>]

On 9/24/26 6:15 PM, Koichiro Den wrote:
> On Tue, Sep 22, 2026 at 11:44:02PM +0200, Marek Vasut wrote:
>> On 9/18/26 5:20 AM, Koichiro Den wrote:
>>> On R-Car, intreq_pcim_sub carries both the integrated MSI receiver and
>>> the controller's reset requests (smlh_req_rst_not, link_req_rst_not), so
>>> the generic DesignWare chained handler reads the MSI status from DBI 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.
>>
>> Out of curiosity, do they trigger SError, and does the firmware (TFA)
>> trap/fix those up in EL3?
> 
> I haven't confirmed whether those DBI accesses trigger an SError.
> The BL31 on the Spider I'm using should be based on rcar-s4_v2.5 [1] from the
> Spider BSP (as I haven't updated it). I just checked that this version also sets
> HANDLE_EA_EL3_FIRST=1, plus plat_ea_handler() is empty. So IIUC an SError would
> be taken to EL3

Yes.

> , and the normal path would return to the kernel without fixing
> the underlying error.

That is correct.

R-Car Gen3 does PCIe link error fixup in TFA, it looks this way:

https://github.com/ARM-software/arm-trusted-firmware/commit/0969397f295621aa26b3d14b76dd397d22be58bf

> And, regardless of whether it's a synchronous abort or an SError:
> - There was no crash report (via report_unhandled_exception) on the console.
> - Once that DBI access in the small window hangs, it never recovers,
>    whereas adding udelay(300) before the access avoids the hang. So I
>    doubt it's just retrying the same access after a transient synchronous
>    abort as well (though I can't rule it out).

( It just crossed my mind, this sounds similar to 0056d29f8c1b ("PCI: 
rcar-gen4: Assure reset occurs before DBI access") )

> [1] https://github.com/renesas-rcar/arm-trusted-firmware/tree/rcar-s4_v2.5
> 
>>
>>> Use the pre-MSI callback to check the APP reset status before DBI is
>>> touched. When a reset request is latched, mask the sources, ack the
>>> request and schedule recovery work. The work calls
>>> pci_host_handle_link_down(), which runs the AER-style recovery and
>>> resets the controller through reset_root_port(). If the reset fails, the
>>> sources stay masked so nothing touches the unrecovered controller.
>>>
>>> Only unmasked status bits are handled and pending latches are cleared
>>> when re-arming, so requests recorded during probe or the reset itself do
>>> not trigger another recovery. Teardown only disables link-down
>>> detection: MSI delivery has to keep working while devices are removed.
>>>
>>> When iMSI-RX is not used (external MSI controller or pci=nomsi), the
>>> DesignWare core does not request intreq_pcim_sub, so request it in the
>>> driver.
>>
>> Would it make sense to request the line unconditionally, to simplify the
>> driver(s) ?
> 
> Yes. The pcie-rcar-gen4 can set pp->msi_irq[0] = -ENODEV just like spear13xx,
> dra7xx and keembay for the same reason. That also removes the need for adding
> .pre_msi_irq addition in patch 4. Some other adjustments might be needed, but I
> believe that is the right and clean direction. I will respin with that in mind.
> 
> Thanks for the review, that helps a lot!

Likewise, thank you for your help !

-- 
Best regards,
Marek Vasut