Re: [Intel-gfx] [PATCH 03/26] drm/irq: Ditch DRIVER_IRQ_SHARED

Daniel Vetter
2019-01-25T16:14:28Z

On Fri, Jan 25, 2019 at 02:46:55PM +0000, Emil Velikov wrote:
> On Thu, 24 Jan 2019 at 16:58, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> >
> > This is only used by drm_irq_install(), which is an optional helper.
> > And the right choice is to set it for all pci devices, and not for
> > everything else.
> >
> Can you please add some information (or reference) why it's the right choice?

pci devices can have a shared interrupt line. That's definitely the case
for legacy pci, and I guess carries over to pcie. msi/msi-x interrupts
will give you dedicated interrupts, but it doesn't really hurt to mark
them as shared.

I guess I could rephrase to state:

"This is only used by drm_irq_install(), which is an optional helper.
For legacy pci devices this is required (due to interrupt sharing without
msi/msi-x), and just making this the default exactly matches the behaviour
of all existing drivers using the drm_irq_install() helpers. In case that
ever becomes wrong drivers can roll their own irq handling, as many
drivers already do (for other reasons like needing a threaded interrupt
handler, or having an entire pile of different interrupt sources)."

That better?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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