Re: [PATCH] drm: Provide drm_set_busid() fallback

[Thierry Reding <thierry.reding@gmail.com>]

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On Fri, Apr 11, 2014 at 07:43:18PM +0200, Daniel Vetter wrote:
> On Fri, Apr 11, 2014 at 03:28:56PM +0200, Thierry Reding wrote:
[...]
> > -	ret = dev->driver->bus->set_busid(dev, master);
> > -	if (ret)
> > -		goto err;
> > +	if (dev->driver->bus && dev->driver->bus->set_busid) {
> > +		ret = dev->driver->bus->set_busid(dev, master);
> > +		if (ret)
> > +			goto err;
> > +	} else {
> 
> Hm, my plan was actually to just provide a drm_dev_setunique to drivers so
> that they can set whatever their userspace wants,

So that would be going one step further and not call drm_set_busid() in
the first place, but rather just let drivers statically assign unique at
probe/load time? Yeah, that makes sense. It's not like the unique string
is going to change at runtime, is it?

> and then have no set_busid implementation here at all for !pci.

Perhaps for PCI there could simply be a common helper to initialize the
unique string in the way it's currently generated by the PCI bus'
implementation of .set_busid(). Even for PCI it's still a static string
that's fixed at probe/load time, isn't it? And it isn't specific per
device, only per drm_bus.

> Some userspace at least uses the unique thing to match for the driver,
> so we need to do the usual bending over backwards to keep it
> consistent.

For new drivers and userspace it should be okay to just match on the
driver name. Any differentiation on a per-device basis is probably
better done using a GET_PARAM ioctl than by parsing a bus ID string.

Or what is userspace doing with the bus ID in the first place?

> The approach with a drm_set_unique helper would also make conversion of
> existing platform and usb drivers easier.

Yeah, I like that better than what this patch does. Is that something
you have already queued up? If not I could take a stab at it.

Thierry

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