From: tomi.valkeinen@ti.com (Tomi Valkeinen) Date: Thu, 9 Jan 2014 10:21:46 +0200 Subject: [PATCH 1/2] ARM: omapfb: add coherent dma memory support In-Reply-To: <79CD15C6BA57404B839C016229A409A83EDB11F5@DBDE04.ent.ti.com> References: <1388409550-10720-1-git-send-email-tomi.valkeinen@ti.com> <1388409550-10720-2-git-send-email-tomi.valkeinen@ti.com> <20140107235951.GH5074@atomide.com> <52CD5D13.9090806@ti.com> <79CD15C6BA57404B839C016229A409A83EDB11F5@DBDE04.ent.ti.com> Message-ID: <52CE5C1A.3070603@ti.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2014-01-09 07:06, Hiremath, Vaibhav wrote: > I am seeing underflow issue on AM43x device if I use omapfb_vram argument. > Did you see this on OMAP? > > I am using "omapfb_vram=10M at 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. Tomi -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 901 bytes Desc: OpenPGP digital signature URL: