Re: [PATCH] PCI: dwc: ep: Cache MSI outbound iATU mapping

[Niklas Cassel <cassel@kernel.org>]

+ Shawn

On Mon, Dec 22, 2025 at 05:53:27PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 12/22/2025 4:41 PM, Niklas Cassel wrote:
> > On Mon, Dec 22, 2025 at 03:28:30PM +0530, Manivannan Sadhasivam wrote:
> > > > Use the MSIX doorbell method which will not use iATU at all,
> > > > dw_pcie_ep_raise_msix_irq_doorbell().
> > > > 
> > > I think this is the safe bet since this feature doesn't seem like an optional
> > > one.
> > > 
> > > Niklas, if you can just fix MSI in this patch and leave out MSI-X for the vendor
> > > drivers to transition to doorbell, I'm OK to merge it. Otherwise, I don't know
> > > how you can reliably fix MSI-X generation with AXI slave interface.
> > FWIW, I did try to simply change:
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > index 8f2cc1ef25e3..00770f9786e3 100644
> > --- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > +++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
> > @@ -319,7 +319,8 @@ static int rockchip_pcie_raise_irq(struct dw_pcie_ep *ep, u8 func_no,
> >          case PCI_IRQ_MSI:
> >                  return dw_pcie_ep_raise_msi_irq(ep, func_no, interrupt_num);
> >          case PCI_IRQ_MSIX:
> > -               return dw_pcie_ep_raise_msix_irq(ep, func_no, interrupt_num);
> > +               return dw_pcie_ep_raise_msix_irq_doorbell(ep, func_no,
> > +                                                         interrupt_num);
> >          default:
> >                  dev_err(pci->dev, "UNKNOWN IRQ type\n");
> >          }
> > 
> > 
> > For the pcie-dw-rockchip driver, but it is not working:
> > [  130.042849] nvme nvme0: I/O tag 0 (1000) QID 0 timeout, completion polled
> > 
> > Without this change, things work.
> > 
> > Perhaps this feature is not an optional one, but at least we will require
> > more changes than a simple one liner.
> Hi Niklas,
> 
> It should be automatic only, no extra configurations should be
> required, I believe your
> HW doesn't support this feature, from spec 6..0a, sec 3.9.1.3
> iMSIX-TX: Integrated MSI-X Transmit (USP)
> I believe your HW is not generated with MSIX_TABLE_EN =1. In that
> case you can't use this feature.

Looking at the RK3588 TRM, it does have register:
USP_PCIE_PL_MSIX_DOORBELL_OFF
Address: Operational Base + offset (0x0248)

Port Logic registers start at offset 0x700 on this SoC,
so 0x700 + 0x248 == 0x948, which matches:
drivers/pci/controller/dwc/pcie-designware.h:#define PCIE_MSIX_DOORBELL         0x948

I don't think the TRM would include this register if the
DWC coere was not generated with MSIX_TABLE_EN=1.

Shawn, any suggestions?
For full thread, see:
https://lore.kernel.org/linux-pci/3b34aa66-a418-4f6b-930a-0728d87d79b6@oss.qualcomm.com/T/#t


FWIW, Krishna Chaitanya, I did try the dw_pcie_ep_raise_msix_irq_doorbell()
change above also with the pci-epf-test EPF driver, and it also caused the
pci-epf-test driver to stop working.


Kind regards,
Niklas