[PATCH v2 2/2] drm/omap: partial workaround for DRA7xx DMM errata i878

[Laurent Pinchart]

Hi Tomi,

On Wednesday, 4 April 2018 13:02:04 EEST Tomi Valkeinen wrote:
> On 04/04/18 12:51, Laurent Pinchart wrote:
> > On Wednesday, 4 April 2018 10:37:05 EEST Tomi Valkeinen wrote:
> >> On 04/04/18 00:11, Laurent Pinchart wrote:
> >>> I assume access to DMM-mapped buffers to be way more frequent than
> >>> access to the DMM registers. If that's the case, this partial workaround
> >>> should only slightly lower the probability of system lock-up. Do you
> >>> have plans to implement a workaround that will fix the problem
> >>> completely ?
> >> 
> >> CPU only accesses memory via DMM when using TILER 2D buffers, which are
> >> not officially supported. For non-2D, the pages are mapped directly to
> >> the CPU without DMM in between.
> > 
> > What is the DMM used for with non-2D then ? Does it need to be setup at
> > all ?
> 
> It creates a contiguous view of memory for IPs without IOMMUs, like DSS.

OK, got it. In that case the CPU accesses don't need to go through the DMM, 
only the device accesses do, as the CPU will go through the MMU. Sorry for the 
noise.

-- 
Regards,

Laurent Pinchart