Hi, list!
With display cards that have more and more hardware on them, (TV-capture, mpeg decoders) etc. that can work independently of oneanother, but share the same DMA engine I've find the need for more than one hardware lock. I've done a simple implementation for the mpeg decoder of the via driver, but that one doesn't cover the DMA case. The question arises "Why should I need to wait for DMA quiescent to check whether the decoder is done with a frame, if there is no decoder data in any of the pending DMA buffers"?
In the VIA / Unichrome case alone there is a need for even more such locks for different parts of the chip if one were to make a clean implementation of drivers for all features that are on the chip.
My idea would be to extend drm with options for multiple locks, and I suspect not only VIA cards could benefit from this. I was thinking of.
1. A separate sarea to contain these locks, to avoid messing up the current sarea with binary incompatibilities as a consequence.
2. Other kernel modules should be able to take and release these locks. (V4L for example).
3. Each DMA buffer is marked (or in the VIA case, each submission to the ring-buffer is marked) wether it accesses the resource that is protected by a certain lock.
4. A resource will become available to a client when the client has taken the lock and there are no pending DMA buffers / parts of buffers that are marked touching this resource.
5. The client is responsible for reinitializing the resource once the lock is taken.
These are just initial thoughts. Is there a mechanism for this in DRM today or could
it be done in a better way?
/Thomas
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