Re: [PATCH v3 3/6] PCI: generic: Quit clobbering our pci_ops.

[David Daney]

On 09/23/2015 01:21 AM, Arnd Bergmann wrote:
> On Tuesday 22 September 2015 16:49:14 David Daney wrote:
> > From: David Daney <david.daney@xxxxxxxxxx>
> >
> > The pci-host-generic driver keeps a global struct pci_ops which it
> > then patches with the .map_bus method appropriate for the bus device.
> > A problem arises when the driver is used for two different types of
> > bus devices, the .map_bus method for the last device probed clobbers
> > the method for all previous devices.  The result, only the last bus
> > device probed has the proper .map_bus, and the others fail.
> >
> > Move the struct pci_ops into the bus specific structure, and
> > initialize it when the bus device is probed.  Keep a copy of the
> > gen_pci_cfg_bus_ops structure, instead of a pointer to a global copy,
>
> This is a very useful change.
>
> > to future proof against the addition of bus specific elements to
> > struct pci_ops.
>
> but I don't like this part. We should just not have bus specific
> elements in pci_ops. We don't really have that here either, except
> that the gen_pci driver had a hack for reusing the same operations
> for things that are actually different.
>
> It's an established practice that anything named '*_operations' is
> meant to be constant and ideally defined as 'static const ... *_ops;'
> in the driver. We could try to enforce this better by marking
> bus->ops as 'const' and changing all the instances of this structure
> accordingly.
>
> > @@ -65,7 +65,11 @@ static void __iomem *gen_pci_map_cfg_bus_cam(struct pci_bus *bus,
> >
> >   static struct gen_pci_cfg_bus_ops gen_pci_cfg_cam_bus_ops = {
> >   	.bus_shift	= 16,
> > -	.map_bus	= gen_pci_map_cfg_bus_cam,
> > +	.ops		= {
> > +		.map_bus	= gen_pci_map_cfg_bus_cam,
> > +		.read		= pci_generic_config_read,
> > +		.write		= pci_generic_config_write,
> > +	}
> >   };
>
> So this is good. We could in theory unify the map_bus functions
> like this now:
>
> static void __iomem *gen_pci_map_cfg_bus(struct pci_bus *bus,
>                                           unsigned int devfn,
>                                           int where)
> {
>          struct gen_pci *pci = bus->sysdata;
> 	struct gen_pci_cfg_bus_ops *ops;
>          resource_size_t idx;
>
> 	ops = container_of(bus->ops, struct gen_pci_cfg_bus_ops, ops);
> 	idx = bus->number - pci->cfg.bus_range->start;
>
>          return pci->cfg.win[idx] + ((devfn << ops->dev_shift) | where);
> }
>
> Not sure if that improves clarity or not, up to Will.
>
> > @@ -234,8 +237,7 @@ static int gen_pci_probe(struct platform_device *pdev)
> >   	}
> >
> >   	of_id = of_match_node(gen_pci_of_match, np);
> > -	pci->cfg.ops = of_id->data;
> > +	pci->cfg.ops = *(struct gen_pci_cfg_bus_ops *)of_id->data;
>
> This is the part that grabbed my attention, we should not do it like this.

I will consider changing this so that a structure copy is not used, 
perhaps as you suggest above.

David Daney.


> 	Arnd

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