Re: 2.6.14-rt4: via DRM errors

[Thomas Hellström <unichrome@shipmail.org>]

>> At one point I was about to implement a scheme for via with a number
>> of similar locks, one for each independent function on the video
>> chip, Like 2D, 3D, Mpeg decoder, Video scaler 1 and 2, so that they
>> didn't have to wait for  eachother. The global lock would then only
>> be taken to make sure that no drawables were touched by the X server
>> or other clients while the lock was held, which would be compatible
>> with how the X server works today. Never got around to do that,
>> however, but the mpeg decoders have a futex scheme to prevent clients
>> stepping on eachother. With that it is possible to have multiple
>> clients use the same hw decoder.
>
> Sounds interesting, but that would be card specific, right?  I mean, on
> some cards the 2d and 3d locks would have to be the same because of
> shared state or whatever, for example.
>
> Jesse
>
Yes. you're right. The idea was to provide an implementation of a set of
locks and context switch / idle hooks that the device-specific driver
could use for whatever part of the chip it wanted, _if_ it wanted to.
When a command stream is submitted, the driver would need to check that
there are only commands for locked part of the chip in the stream. There
would also need to be a mechanism to check whether there are pending DMA
commands corresponding to a particular lock, to avoid having to make DMA
quiescent in unnecessary cases. Lock values would reside in a separate
shared memory area. However, a bit complicated and too little time.

/Thomas.


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