Re: [PATCH 4/4] ARM: shmobile: ag5evm, ap4: Make use of irq index enum

Simon Horman
2011-08-19T05:20:11Z

On Fri, Aug 19, 2011 at 01:16:09PM +0900, Magnus Damm wrote:
> On Fri, Aug 19, 2011 at 10:10 AM, Simon Horman <horms@verge.net.au> wrote:
> > This is intended to make it easier to correctly order IRQs.
> >
> > As suggested by Guennadi Liakhovetski.
>
> > --- a/arch/arm/mach-shmobile/board-ag5evm.c
> > +++ b/arch/arm/mach-shmobile/board-ag5evm.c
> > @@ -352,15 +352,15 @@ static struct resource sdhi0_resources[] = {
> >                .end    = 0xee1000ff,
> >                .flags  = IORESOURCE_MEM,
> >        },
> > -       [1] = {
> > +       [1 + SH_MOBILE_SDHI_IRQ_CARD_DETECT] = {
> >                .start  = gic_spi(83),
> >                .flags  = IORESOURCE_IRQ,
> >        },
> > -       [2] = {
> > +       [1 + SH_MOBILE_SDHI_IRQ_SDCARD] = {
> >                .start  = gic_spi(84),
> >                .flags  = IORESOURCE_IRQ,
> >        },
> > -       [3] = {
> > +       [1 + SH_MOBILE_SDHI_IRQ_SDIO] = {
> >                .start  = gic_spi(85),
> >                .flags  = IORESOURCE_IRQ,
> >        },
>
> Hm...
>
> So I know you guys have been discussing this back and forth, so I'm
> not sure if jumping in to this thread makes things any better. But
> anyhow, here are my opinions. Feel free to ignore them. =)
>
> First of all, having some kind of association with each IRQ is a good
> thing. I am however not convinced that using the index number of the
> platform device resource irq is the best option. Consider the case
> when someone modifies the SDHI resource in the code above to only
> include this interrupt:
>
> [1 + SH_MOBILE_SDHI_IRQ_SDCARD] = {
> .start = gic_spi(84),
> .flags = IORESOURCE_IRQ,
> },
>
> >From my point of view, the common sense for this would be that only
> the SDCARD interrupt would be enabled and the rest would be disabled
> since they are unspecified. However, with the current code the
> behavior would be something else, and since the index number of SDCARD
> is not matching it will be detected as CARD_DETECT.
>
> So isn't it really ugly to depend on the number of IRQs when they are
> supposed to be used as an index? I've been toying around with this
> driver for a few years now, and when I have a hard time creating
> correct platform data then it's _probably_ a sign that there must be
> better ways to implement this.
>
> I would propose just adding interrupts in struct resource [] as usual,
> and then have thee separate flags in the platform data for each
> interrupt type. If the number of IRQ bits set in the platform data
> flags doesn't match the number of interrupt resources then return
> error. If they match then simply go through each flag set in the
> platform data flags and assign next available interrupt resource. And
> if no flags are set then go for the combined interrupt handler for all
> available interrupt resources.
>
> That's what I would do at least. Any other ideas? Perhaps just keep an
> array of interrupt numbers in the platform data as the sh-sci driver
> does and use the fixed indexes there if non-zero?

Hi Magnus,

unfortunately during the course of the review of this series a number
of changes have crept in which I regard as being tangential to the
goal of the series - which is to introduce broken-out handlers (I have
already introduce support for broken-out IRQ sources).

One area where such changes have occurred is in the subtle altering of the
list of IRQ sources that it is valid to supply (again, support for
broken-out IRQ sources is not introduced by this series).

With regards to your comment and example above. I believe that your
understanding of my code is incorrect. The configuration you suggest will
be rejected because CARD_DETECT is not supplied, not because of an index
miss-match. It could be made acceptable within the current framework by
simply loosening up the logic a little (specifically to allow CARD_DETECT
to be omitted even if only one other IRQ source is supplied). Incidently,
I think that would make sense but Guennadi specifically asked for that
combination to be regarded as invalid.

You suggestion to not rely on the array offset is an interesting one
and perhaps it would make things easier (to understand). But I don't
believe it would entirely eliminate the possibility of creating bogus
platform data. And in any case I believe it is tangential to the aim
of this series - to introduce broken-out handlers.

Moreover, I think that there needs to be some agreement between Guennadi
and yourself with regards to what IRQ combinations are valid before I (or
anyone else) can implement something that is acceptable to you both. And
I think that in the mean time the current implementation is reasonable
given that it works with all current use-cases (and several non-existent
ones too).

In short, can we have this discussion in the context of further enhancements?