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SubjectRe: [PATCH 3/8] Add a mfd IPUv3 driver
On Tue, Mar 01, 2011 at 11:27:49AM +0100, Arnd Bergmann wrote:
> On Tuesday 01 March 2011, Sascha Hauer wrote:
>
> > When turning this into a kms driver moving the source code will be the
> > smallest problem I guess.
> > I have no preference where to put this code. First it was in
> > drivers/mfd/ and it felt wrong because there seems to be too much code
> > in it a mfd maintainer shouldn't be bothered with. drivers/video/ seems
> > to be wrong because this code will probably support cameras which belong
> > to drivers/media/video/. So if there's consensus on drivers/gpu/ I will
> > happily put it there.
> > What directory do you suggest? drivers/gpu/ or some subdirectory
> > (drm/vga)?
>
> I'd suggest a subdirectory of drivers/gpu/, e.g.
> drivers/gpu/embedded/imx-ipu/. Alan is currently adding a driver
> for the Intel GMA500, and there are others (TI, ST-Ericsson, ...)
> that fit in a similar category of complex graphics subsystems
> without an actual GPU core. I think they should all go to the same
> place.
>
> > > The interrupt logic needs some comments. What are you trying to achieve here?
> >
> > The IPU has 463 status bits which can trigger an interrupt. Most
> > of them are associated to channels, some are general interrupts. My
> > problem is that I don't know how the interrupts will be used by drivers
> > later. Most drivers will probably use only one interrupt but others
> > will be interested in a larger group of interrupts. So I decided to
> > use a bitmap allowing each driver to register for groups of event
> > it is interested in.
>
> Ok, I see. So you essentially have a huge nested interrupt controller
> and try to be clever about the possible use cases, which may be the
> right choice, but apparently you don't know that yet because not
> all the drivers have been written at this point.
>
> Taking one step back from this, have you considered making this
> a regular interrupt controller? That would make the client drivers
> more standard -- you could define the interrupt numbers as resources
> of a platform device or in the device tree, for instance.
> The cost might be more complex code, e.g. when a device requires
> many interrupts, but I think it will be at least as efficient
> at run-time, and less surprising for readers and authors of
> client drivers.

I thought about this, but hesitated to increase NR_IRQS by 463. Do you
think we should do this instead?

Sascha

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