[alsa-devel] [PATCH 7/8] ALSA: pcm: Add card sync_irq field

[Sridharan, Ranjani]

On Mon, Nov 18, 2019 at 10:54 AM Takashi Iwai <tiwai at suse.de> wrote:

> On Mon, 18 Nov 2019 17:38:49 +0100,
> Pierre-Louis Bossart wrote:
> >
> >
> >
> > On 11/17/19 2:53 AM, Takashi Iwai wrote:
> > > Many PCI and other drivers performs snd_pcm_period_elapsed() simply in
> > > its interrupt handler, so the sync_stop operation is just to call
> > > synchronize_irq().  Instead of putting this call multiple times,
> > > introduce the common card->sync_irq field.  When this field is set,
> > > PCM core performs synchronize_irq() for sync-stop operation.  Each
> > > driver just needs to copy its local IRQ number to card->sync_irq, and
> > > that's all we need.
> >
> > Maybe a red-herring or complete non-sense, but I wonder if this is
> > going to get in the way of Ranjani's multi-client work, where we could
> > have multiple cards created but with a single IRQ handled by the
> > parent PCI device?
> >
> > Ranjani, you may want to double-check this and chime in, thanks!
>
> The synchronize_irq() is fairly safe to call multiple times, and I
> don't think any problem by invoking it for multi-clients sharing the
> same IRQ.  For example, Digigram miXart driver creates multiple card
> objects from a single PCI entry, and I already thought of that
> possibility; they set the same card->sync_irq value to all card
> objects, which eventually will call synchronize_irq() multiple times.
>  From the performance POV, this shouldn't be a big problem, because
> the place calling this is only at hw_params, prepare and hw_free,
> neither are hot-path.
>
Thanks for the clarification, Takashi. But just wondering how would one
pass on the sync_irq when the snd_card is created? Typically in the case of
the Intel platforms, the card->dev points to the platform device for the
machine driver that registers the card and the PCI device is the parent of
the machine drv platform device.

Thanks,
Ranjani