[PATCH] drm/vmwgfx: Stop requesting the pci regions

[Zack Rusin]

On Tue, 2022-01-18 at 20:00 +0100, Javier Martinez Canillas wrote:
> Hello Zack,
> 
> On 1/17/22 19:03, Zack Rusin wrote:
> > From: Zack Rusin <zackr at vmware.com>
> > 
> > When sysfb_simple is enabled loading vmwgfx fails because the regions
> > are held by the platform. In that case
> > remove_conflicting*_framebuffers
> > only removes the simplefb but not the regions held by sysfb.
> > 
> 
> Indeed, that's an issue. I wonder if we should drop the IORESOURCE_BUSY
> flag from the memory resource added to the "simple-framebuffer" device
> ?

I think this is one of those cases where it depends on what we plan to
do after that. Sementically it makes sense to have it in there - the
framebuffer memory is claimed by the "simple-framebuffer" and it's
busy, it's just that it creates issues for drivers after unloading. I
think removing it, while making things easier for drivers, would be
confusing for people reading the code later, unless there's some kind
of cleanup that would happen with it (e.g. removing IORESOURCE_BUSY
altogether and making the drm drivers properly request their
resources). At least by itself it doesn't seem to be much better
solution than having the drm drivers not call pci_request_region[s],
which apart from hyperv and cirrus (iirc bochs does it for resources
other than fb which wouldn't have been claimed by "simple-framebuffer")
is already the case. 

I do think we should do one of them to make the codebase coherent:
either remove IORESOURCE_BUSY from "simple-framebuffer" or remove
pci_request_region[s] from hyperv and cirrus.



> > Like the other drm drivers we need to stop requesting all the pci
> > regions
> > to let the driver load with platform code enabled.
> > This allows vmwgfx to load correctly on systems with sysfb_simple
> > enabled.
> > 
> 
> I read this very interesting thread from two years ago:
> 
> https://lkml.org/lkml/2020/11/5/248
> 
> Maybe is worth mentioning in the commit message what Daniel said there,
> that is that only a few DRM drivers request explicitly the PCI regions
> and the only reliable approach is for bus drivers to claim these.

Ah, great point. I'll update the commit log with that.

> > Signed-off-by: Zack Rusin <zackr at vmware.com>
> > Fixes: 523375c943e5 ("drm/vmwgfx: Port vmwgfx to arm64")
> > Cc: dri-devel at lists.freedesktop.org
> > Cc: <stable at vger.kernel.org>
> > Reviewed-by: Martin Krastev <krastevm at vmware.com>
> > ---
> 
> The patch looks good to me, thanks a lot for fixing this:
> 
> Reviewed-by: Javier Martinez Canillas <javierm at redhat.com>

Thanks for taking a look at this, I appreciate it!

z