Re: [PATCH v8 8/9] PCI: endpoint: pci-epf-test: Reuse pre-exposed doorbell targets

[Koichiro Den]

On Tue, Feb 17, 2026 at 11:15:08AM +0100, Niklas Cassel wrote:
> Hello Koichiro,
> 
> On Tue, Feb 17, 2026 at 05:06:00PM +0900, Koichiro Den wrote:
> > pci-epf-test advertises the doorbell target to the RC as a BAR number
> > and an offset, and the RC rings the doorbell with a single DWORD MMIO
> > write.
> > 
> > Some doorbell backends may report that the doorbell target is already
> > exposed via a platform-owned fixed BAR (db_msg[0].bar/offset). In that
> > case, reuse the pre-exposed window and do not reprogram the BAR with
> > pci_epc_set_bar().
> > 
> > Also honor db_msg[0].irq_flags when requesting the doorbell IRQ, and
> > only restore the original BAR mapping on disable if pci-epf-test
> > programmed it.
> > 
> > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > ---
> 
> (snip)
> 
> > @@ -753,22 +771,33 @@ static void pci_epf_test_enable_doorbell(struct pci_epf_test *epf_test,
> >  	reg->doorbell_data = cpu_to_le32(msg->data);
> >  	reg->doorbell_bar = cpu_to_le32(bar);
> >  
> > -	msg = &epf->db_msg[0].msg;
> > -	ret = pci_epf_align_inbound_addr(epf, bar, ((u64)msg->address_hi << 32) | msg->address_lo,
> > -					 &epf_test->db_bar.phys_addr, &offset);
> > +	if (db->bar == NO_BAR) {
> > +		ret = pci_epf_align_inbound_addr(epf, bar,
> > +						 ((u64)msg->address_hi << 32) |
> > +						 msg->address_lo,
> > +						 &epf_test->db_bar.phys_addr,
> > +						 &offset);
> >  
> > -	if (ret)
> > -		goto err_free_irq;
> > +		if (ret)
> > +			goto err_free_irq;
> > +	}
> 
> I tried this series on Rock5b (RK3588), and was surprised to see the doorbell
> test case still failing.

Thank you very much for testing, and apologies for not being able to test on
RK3588 on my side right now.

> 
> 
> > +
> > +	if (size_add(offset, sizeof(u32)) > epf->bar[bar].size)
> > +		goto err_doorbell_cleanup;
> 
> It turns out that this check is the reason for it still failing.
> 
> You see, for a BAR that is marked as BAR_RESERVED, pci-epf-test will not
> allocate backing memory, so epf->bar[bar].size will be 0.
> 
> If I removed this check, I could get the test case to pass.
> 
> As I suggested in my previous email, perhaps this check is better suited
> in pci_epf_alloc_doorbell(). (As a DWORD alignment check inside
> pci_epf_alloc_doorbell(). pci_epf_alloc_doorbell() could itself return
> error if the doorbell is not DWORD aligned.)

Yes, and I mentioned there I would reconsider this when respinning this feature
series. For reference:
https://lore.kernel.org/linux-pci/jcjson6zedvhkpctwzfao2wfaaujtdfqsnnm3k25e2vpz2evf4@hbsegnyevisu/
I hadn't noticed the bar.size==0 possibility at that time.

I agree that this check is better placed in pci_epf_alloc_doorbell().
I'll respin accordingly.

Thanks again for the testing and review,
Koichiro

> 
> That way, you could remove this check from pci_epf_test_enable_doorbell(),
> and we don't need to care about epf->bar[bar].size.
> 
> 
> Kind regards,
> Niklas