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Currently, each process holding an open TegraDRM channel reserves for itself one of the limited number of hardware memory contexts. Attempting to allocate a channel when all contexts are in use results in failure. While we cannot have more contexts than the hardware supports in active use, idle channels don't necessarily need to have a backing memory context. As such, in this patch, we add another layer to allow hardware memory contexts to be "stolen away" by channels that are in active use, from idle processes. The way this is implemented, is by keeping track of memory mappings on each abstracted memory context. If we need to steal that memory context's backing hardware context, we unmap everything from it and give it away. When that abstracted memory context is needed again (re-activated), we attempt to allocate or steal another hardware context and re-map the previously unmapped buffers. Unfortunately, this means additional overhead and unpredictability at submit time. Submit can fail if we cannot re-allocate a backing memory context. Future work includes a provision for un-stealable backing hardware memory contexts for processes requiring more determinism, as well as optimization and cosmetic improvements. Bug 4403250 Bug 4399310 Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com> Change-Id: I3d13e3476f1bff3c4757152254496cddaaafd76a Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/3058905 Reviewed-by: Santosh BS <santoshb@nvidia.com> GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com> Reviewed-on: https://git-master.nvidia.com/r/c/linux-nv-oot/+/3227749 GVS: buildbot_gerritrpt <buildbot_gerritrpt@nvidia.com> Tested-by: Dane Liu <danel@nvidia.com> Reviewed-by: Bibek Basu <bbasu@nvidia.com>