-----Original Message-----
From: Valkeinen, Tomi
Sent: Thursday, January 09, 2014 1:52 PM
To: Hiremath, Vaibhav; Ivaylo Dimitrov
Cc: Tony Lindgren; linux-omap@vger.kernel.org; linux-arm-
kernel@lists.infradead.org; linux-fbdev@vger.kernel.org
Subject: Re: [PATCH 1/2] ARM: omapfb: add coherent dma memory support

On 2014-01-09 07:06, Hiremath, Vaibhav wrote:

quoted

I am seeing underflow issue on AM43x device if I use omapfb_vram argument.
Did you see this on OMAP?

I am using "omapfb_vramM@0xA0000000", and I believe it is correct way

of usage.

Hmm ok... The AM4x seems to have issues anyway, as we're seeing underflows
easily in other situations also.

Well, there's a small difference in the allocation. The normal dma alloc uses
dma_alloc_attrs() and passes DMA_ATTR_WRITE_COMBINE as a flag, whereas
allocating from the absolute address just uses the piece of memory. I couldn't
find how to set write-combine for the abs memory area.

Then again, that's for CPU caching, so I don't see why it would affect DSS as
such (but that's still something we should measure, cpu read/write perf for
normal and abs allocation).

The only thought I have is that somehow the reserved memory area is missing
some configuration that is done for the rest of the memory. But that's purely a
guess, this is totally out of my area of expertise...

Vaibhav, just to be sure, can you run both with normal dma_alloc and with the
reserve, and verify that the dispc register dumps are the same?
I don't see how they could be different, but just to be sure.

Will check and update you shortly.

Thanks,
Vaibhav