Re: [PATCH] linux/pci.h: add a dummy implement for pci_clear_master()

[Sui Jingfeng]

Hi,

On 2023/6/1 01:16, Bjorn Helgaas wrote:
> On Wed, May 31, 2023 at 12:25:10PM +0800, Sui Jingfeng wrote:
> > On 2023/5/31 04:11, Bjorn Helgaas wrote:
> > > On Tue, May 30, 2023 at 06:16:55PM +0800, Sui Jingfeng wrote:
> > > > As some arch(m68k for example) doesn't have config_pci enabled, drivers[1]
> > > > call pci_clear_master() without config_pci guard can not built.
> > > >
> > > >      drivers/gpu/drm/etnaviv/etnaviv_pci_drv.c:
> > > >      In function 'etnaviv_gpu_pci_fini':
> > > > > > drivers/gpu/drm/etnaviv/etnaviv_pci_drv.c:32:9:
> > > >      error: implicit declaration of function 'pci_clear_master';
> > > >      did you mean 'pci_set_master'? [-Werror=implicit-function-declaration]
> > > >         32 |         pci_clear_master(pdev);
> > > >            |         ^~~~~~~~~~~~~~~~
> > > >            |         pci_set_master
> > > >      cc1: some warnings being treated as errors
> > > >
> > > > [1] https://patchwork.freedesktop.org/patch/539977/?series=118522&rev=1
> > > I don't mind adding a stub if it's needed, but I don't understand why
> > > it's needed here.
> > For a single driver that supports both platform devices and PCI devices,
> >
> > Sometimes there is no way to separate the PCI driver part and the platform
> > driver part cleanly and clearly.
> >
> > For example, the module_init() and module_exit() functions,
> >
> > where we have to register PCI drivers and platform drivers there.
> >
> > We can't simply let the entire driver depend on PCI in Kconfig,
> >
> > This will make this driver unable to compile, which it's originally could.
> >
> > The PCI core could do such a thing for us, and
> >
> > There is no need to introduce a driver-specific guard then.
> >
> >
> > There is already a dummy stub for pci_set_master().
> >
> > Therefore, pci_clear_master() should also have a counterpart.
> >
> > They should emerge in pairs.
> >
> > This could probably eliminate pain for PCI driver writers,
> >
> > This patch is still useful.
> >
> >
> > >    The caller is in etnaviv_pci_drv.c, and if I
> > > understand the patch at [1], etnaviv_pci_drv.c is only compiled when
> > > CONFIG_PCI=y.
> > Yes, you are right. This is the right thing to do for the driver, though.
> >
> > Pure PCI device driver does not need to worry about this.
> >
> > Like drm/ast, drm/amdgpu, drm/radeon, etc.
> >
> > But drm/etnaviv is special; it's a platform driver that could pass the
> > compile test originally.
> >
> >
> > When patching it (Etnaviv) with PCI device driver support,
> >
> > This forces the PCI driver writer to add another config option.
> >
> > (which depends on the PCI config option.) in the Kconfig.
> >
> > For my case, it's theDRM_ETNAVIV_PCI_DRIVER config option.
> So if I understand correctly, you would prefer not to add the
> DRM_ETNAVIV_PCI_DRIVER config option, and if we add this stub, you
> won't need to add it?
>
> That's a good reason to add this patch.

Yes, please add this patch.

Otherwise, other people may suffer from the same issue someday.

After  this patch added,  I will try respin my etnaviv patch set.

If the PCI core could shield the hazard for us.

I would prefer my etnaviv don't introduce any config option.

Compile anywhere at any case.

> Bjorn

--
Jingfeng