Re: [PATCH 4/6] g_NCR5380: Add IRQ auto-configuration for HP C2502

[Ondrej Zary <linux@rainbow-software.org>]

On Thursday 03 November 2016, Finn Thain wrote:
> On Wed, 2 Nov 2016, Ondrej Zary wrote:
> > > Also, you've ignored the irq module parameters. From the user's point
> > > of view, surely the least surprising thing is to attempt to configure
> > > the card for whatever irq the user asked for.
> >
> > I haven't. NCR5380_find_irq is only called when irq is set to IRQ_AUTO.
>
> My mistake.
>
> > > If the specified irq isn't supported by the board, just log an error
> > > and fail. If you want to be user friendly, print a message to tell
> > > them what irqs the card supports.
> >
> > If the IRQ is not supported (or does not work), user gets a warning and
> > the driver continues with IRQ disabled.
> >
> > > If the user asks for IRQ_AUTO, just configure the board for a
> > > hard-coded default, say 9, and print a warning message to say so.
> >
> > The card is almost Plug&Play. The base address is already configured
> > automatically by the driver so doing the same for IRQ makes sense.
>
> Why don't we see any other drivers doing this?

Many ISA sound card drivers do this - there's even a function for this:
static int snd_legacy_find_free_irq(int *irq_table)

Unfortunately, it's defined in ALSA headers and even protected with an #ifdef.

> If the card was really plug and play, I expect we would just call
> pnp_irq(), as the other PNP drivers do.

The card predates the PnP standard so we can't.

> > > Either way, if request_irq fails just continue with NO_IRQ, as per
> > > usual.
> > >
> > > To me that's the most flexible and least surprising behaviour. But
> > > again, if someone with more ISA knowledge wishes to weigh in, that's
> > > fine too.



-- 
Ondrej Zary