linux-kernel - Re: [PATCH] linux/pci.h: add a dummy implement for pci_clear

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Message-ID: <ZHeA6eB5FocARdwl@bhelgaas>
Date:   Wed, 31 May 2023 12:16:25 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sui Jingfeng <suijingfeng@...ngson.cn>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] linux/pci.h: add a dummy implement for pci_clear_master()

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.

Bjorn