[alsa-devel] [PATCH v4 5/7] ASoC: intel - add Skylake HDA audio driver

[Takashi Iwai]

At Tue, 2 Jun 2015 12:10:34 +0100,
Mark Brown wrote:
> 
> On Tue, Jun 02, 2015 at 12:48:50PM +0200, Takashi Iwai wrote:
> > Mark Brown wrote:
> 
> > > Why does the driver care though?  IRQF_SHARED is advertising the
> > > capabilities of the hander, not a requirement on the hardware - if the
> > > interrupt physically can't be shared then the ability to share it will
> > > never get used but that shouldn't matter.
> 
> > Because the kernel doesn't guarantee the exclusiveness of irq handler
> > registration as long as you pass IRQF_SHARED.  That is, if we keep
> > IRQF_SHARED and another driver tries to request_irq() for the same irq
> > with again IRQF_SHARED.  But this shouldn't happen with MSI.
> 
> Sure, but how could that happen (given that the interrupt physically
> can't be shared) and surely individual client drivers are the wrong
> place to do this -

Oh how can you trust BIOS setup? :)  A wrong numbered IRQ is a most
frequently seen problem (mostly not about MSI, though).

> it's not like MSI is the only interrupt type that has
> trouble with sharability, if this is an issue we need to have checks and
> enforcement for I'd expect the interrupt controller to be flagging
> itself as unsharable.

Rather the sharable interrupt is exceptional, I'd say.  That's the
reason we have IRQF_SHARED, not IRQF_EXCLUSIVE.


Takashi