Re: [PATCH] drm/i915: Add OACONTROL to the command parser register whitelist.

[Kenneth Graunke <kenneth@whitecape.org>]

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On 03/27/2014 03:44 PM, Daniel Vetter wrote:
> On Thu, Mar 27, 2014 at 10:34 PM, Kenneth Graunke <kenneth@whitecape.org> wrote:
>> Why are we parsing batches with I915_EXEC_SECURE at all?  Secure batches
>> are only issued from trusted code which is guaranteed to be running as
>> root.  I don't see any benefit to scanning those batches, and there's
>> definitely overhead.
>>
>> I mean, sure, it may be reasonable in the short term as a way to test
>> the command parser, but I certainly hope we don't *ship* that.
> 
> Everyone runs X as root, but I kinda want X to also be able to run as
> non-root. The cmd parser has a special list of drm master register
> lists which should allow this, but if we just bypass the cmd parser
> for all normal X installs we'll have 0 test coverage on this. Which
> means broken like hell.
> 
> Hence I actually intend to ship this, yes. Chris doesn't like it either really.
> -Daniel

Seriously?  Hurt performance on every user's system just so you can test
things?  That a classic case of the tail wagging the dog.

Why not make a i915.enable_cmd_parser=2 value which enables it all the
time and use that when running igt?  Clearly being able to test this is
valuable, but enabling it universally is *not* OK.


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