Panthor DRM Driver For Arm Mali Graphics Working On User Submission Handling

Arm engineer Mihail Atanassov proposed a set of "request for comments" patches this week for adding user submission support to the Panthor DRM driver that is used for handling newer Arm Mali graphics under Linux. This would allow user-space more easily to submit work directly to the GPU hardware without kernel intervention for better performance and management capabilities.

The RFC patches posted on Monday are the initial design for handling user submission support with this newer Direct Rendering Manager driver. Atanassov explains of the Panthor user submission work:

"This series implements a mechanism to expose Mali CSF GPUs' queue ringbuffers directly to userspace, along with paraphernalia to allow userspace to control job synchronisation between the CPU and GPU.

The goal of these changes is to allow userspace to control work submission to the FW/HW directly without kernel intervention in the common case, thereby reducing context switching overhead. It also allows for greater flexibility in the way work is enqueued in the ringbufs. For example, the current kernel submit path only supports indirect calls, which is inefficient for small command buffers. Userspace can also skip unnecessary sync operations.

This is still a work-in-progress, there's an outstanding issue with multiple processes using different submission flows triggering scheduling bugs (e.g. the same group getting scheduled twice), but we'd love to gather some feedback on the suitability of the approach in general and see if there's a clear path to merging something like this eventually."

Those interested in this user submission work for the Arm Panthor driver can find the RFC patches under review on the mailing list.

Panthor was initially upstreamed in Linux 6.10 as the new DRM driver for supporting newer Arm Mali graphics requiring the Command Stream Frontend (CSF) firmware as a fundamental design shift compared to the earlier Mali graphics hardware.