[PATCH] drm: hdlcd: allow HDLCD to be used without interrupt

[Liviu Dudau]

On Tue, Aug 29, 2017 at 05:48:24PM +0100, Russell King - ARM Linux wrote:
> On Tue, Aug 29, 2017 at 02:33:52PM +0100, Liviu Dudau wrote:
> > I've worked with Vladimir Murzin inside ARM to try to sort out problems
> > on the board like the one that you have. He's got to a point where the HDLCD
> > starts correctly after adding a non-fixed pxlclk source, but then the rest of
> > the setup is semi-useless without a working IRQ because DRM atomic calls
> > will give you a vblank timeout splat everytime you invoke them. So I'm
> > not sure how you want to progress with this patch, as not having an IRQ
> > line means you will not get any vblank interrupts and you can't use the
> > driver with userspace that calls DRM API.
> > 
> > The RTL guys are apparently working on a fix, but I have no ETA or
> > details on when they are going to do.
> 
> It sounds then like this patch doesn't make sense - so I'm happy
> for it to be dropped.  It's something to bear in mind in the future
> when folk decide whether to adopt fbdev or DRM support for hardware
> that gets used in MMU-less hardware...

I don't think this has anything to do with the presence of a MMU or not.

If you don't have a way of signaling back to userspace when a vblank event
has occured then the driver needs to have additional code to reject ioctls
that depend on that functionality. So your patch is not wrong, it just needs
more code to be really useful.

Best regards,
Liviu

> 
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