[PATCH 1/2] ARM: omapfb: add coherent dma memory support

[Hiremath, Vaibhav]

> -----Original Message-----
> From: Valkeinen, Tomi
> Sent: Thursday, January 09, 2014 1:57 PM
> To: Hiremath, Vaibhav; Ivaylo Dimitrov; Ivaylo Dimitrov
> Cc: Tony Lindgren; linux-omap at vger.kernel.org; linux-arm-
> kernel at lists.infradead.org; linux-fbdev at vger.kernel.org
> Subject: Re: [PATCH 1/2] ARM: omapfb: add coherent dma memory support
> 
> On 2014-01-09 10:08, Hiremath, Vaibhav wrote:
> 
> > No, that's what is causing issue to me. Can you try predefined address flow?
> > Just to highlight, I get UNDERFLOW during boot itself, immediately when it
> gets mapped to userspace.
> >
> > Boot LOG:
> >
> 
> > [    4.822549] Freeing unused kernel memory: 440K (c0919000 - c0987000)
> > [    5.276615] OMAPFB: pan_display(0)
> > [    5.276625] OMAPFB: setcmap
> > [    5.276635] OMAPFB: setcmap
> > [    5.293518] OMAPFB: user mmap region start a0000000, len 1536000, off 0
> > [    5.300171] omapdss APPLY error: FIFO UNDERFLOW on gfx, disabling the
> overlay
> 
> Hmm that's interesting... So you have some tool that's ran early, which draws
> something on the screen? Or maybe that's X starting?
> 

It's initial demo, not sure whether you heard of MATRIX demo. I am running Matrix demo
As part of init script.

> Ah... I think I understand now. As I mentioned, AM4x has issues already.
> I think the CPU/others can block DSS when accessing memory. So, if we have
> bad caching for the mapped framebuffer, the CPU will use more bandwidth
> when reading/writing to it, and that will cause DSS to underflow.
> 

Yeah, AM4x already has some issues but I am comparing normal dma_alloc and reserved
Memory and I see different behavior and it could be due to bad caching for the mapped buffers.

Thanks,
Vaibhav