RE: [PATCH v2 6/6] misc: pci_endpoint_test: Add Device ID for R-Car V4H PCIe controller

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Hi Geert-san,

> From: Geert Uytterhoeven, Sent: Wednesday, March 27, 2024 5:12 PM
> 
> Hi Shimoda-san,
> 
> On Tue, Mar 26, 2024 at 6:47 AM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@renesas.com> wrote:
> > > From: Frank Li, Sent: Tuesday, March 26, 2024 12:21 PM
> > > On Tue, Mar 26, 2024 at 11:45:40AM +0900, Yoshihiro Shimoda wrote:
> > > > Add Renesas R8A779G0 in pci_device_id table so that pci-epf-test
> > > > can be used for testing PCIe EP on R-Car V4H.
> > > >
> > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > > > Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > > > ---
> > > >  drivers/misc/pci_endpoint_test.c | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> > > > index c38a6083f0a7..2fa3c6473c7d 100644
> > > > --- a/drivers/misc/pci_endpoint_test.c
> > > > +++ b/drivers/misc/pci_endpoint_test.c
> > > > @@ -83,6 +83,7 @@
> > > >  #define PCI_DEVICE_ID_RENESAS_R8A774C0             0x002d
> > > >  #define PCI_DEVICE_ID_RENESAS_R8A774E1             0x0025
> > > >  #define PCI_DEVICE_ID_RENESAS_R8A779F0             0x0031
> > > > +#define PCI_DEVICE_ID_RENESAS_R8A779G0             0x0030
> > > >
> > > >  static DEFINE_IDA(pci_endpoint_test_ida);
> > > >
> > > > @@ -1005,6 +1006,9 @@ static const struct pci_device_id pci_endpoint_test_tbl[] = {
> > > >     { PCI_DEVICE(PCI_VENDOR_ID_RENESAS, PCI_DEVICE_ID_RENESAS_R8A779F0),
> > > >       .driver_data = (kernel_ulong_t)&default_data,
> > > >     },
> > > > +   { PCI_DEVICE(PCI_VENDOR_ID_RENESAS, PCI_DEVICE_ID_RENESAS_R8A779G0),
> > > > +     .driver_data = (kernel_ulong_t)&default_data,
> > > > +   },
> > >
> > > You use default_data, why need new device_id? I think you can use 0x0031
> > > to do test.
> >
> > I thought we can add a new device_id freely like other devices.
> > Since the PCIe controller's endpoint mode can configure the device id,
> > I can use 0x0031 to do test though.
> 
> Can it?

Yes, the following function can write the device id in endpoint mode.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/dwc/pcie-designware-ep.c?h=v6.9-rc1#n108

> The documentation for the PCICONF0Fi register states both the
> DEVICE_ID and VENDOR_ID bits are read-only.

You're correct. The documentation (R-Car V4H hardware manual) said these bits are read-only.
However, actual hardware IP seems to allow writing this register if the write protect is disabled in endpoint mode.

Best regards,
Yoshihiro Shimoda

> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds