[PATCH 05/19] drm: move dev_mapping to the minor node

[Ilija Hadzic]

On Fri, 20 Apr 2012, Dave Airlie wrote:

> On Thu, Apr 12, 2012 at 7:19 PM, Ilija Hadzic
> <ihadzic at research.bell-labs.com> wrote:
>> Make dev_mapping per-minor instead of per device. This is
>> a preparatory patch for introducing render nodes. This
>> will allow per-node instead of per-device mapping range,
>> once we introduce render nodes.
>
> One problem is this introduces a ttm/drm dependency that we don't
> really have so far.
>

Sorry for a belated follow-up (I was busy with something else). I 
understand the concern and I think that the patch can be reworked such 
that it does not introduce the dependency. What introduces the dependency 
is a call to drm_unmap_mapping in ttm_bo_unmap_virtual. If the patch is 
reworked such that the minor tracks i_mapping pointer instead of the whole 
drm_device structure, the need for drm_unmap_mapping may be eliminated, 
which in turn will take care of the dependency.

That brings me to a question for you. The patch from which I derived this 
is your patch 7c5cc4f63556e351e9e5980ed22accad410e3fdc (on your original 
render-nodes branch). That's where you introduced drm_unmap_mapping 
function, which calls unmap_mapping_range for every minor known to the 
system.

Why was that necessary at first place ? I mean we don't do the eqivalent 
of that currently when there are multiple physical GPUs in the system, so 
I don't quite get why introduction of multiple minors would require to go 
through the whole list of minors. If that's a "just in case"/"just to be 
safe" kind of thing, then I think we may be able to just call 
drm_unmap_mapping from the driver that needs to call it and only for the 
minor in question.

If we can do that, then the patch will in principle look the same to what 
the current code does, except that dev_mapping will be in the minor 
structure and there will ne no new dependencies introduced. The patch will 
also be simpler that way.

-- Ilija