[v2,0/2] drm/panthor: Fix panthor+FEX-Emu

Message

Boris Brezillon April 17, 2025, 2:49 p.m. UTC

Hello,

This is an attempt a couple bugs exposed by FEX-Emu. The first one
is pretty trivial and should be uncontroversial, since it's just
a missing padding field in one of our uAPI structs. We are getting
away with it on arm32 because of the alignment rules provided by
the Arm ABI, but x86 has relaxed constraints for u64 fields, and
this bug is definitely hit when running a 32-bit x86 mesa binary
under FEX Emu.

The second fix is addressing a problem we have because FEX-Emu is
an aarch64 process executing 32-bit x86 code, meaning the check
we do on the is-32bit-task check we do to figure out the MMIO
offset seen by the user won't work. In order to fix that, we add
an ioctl to let the user explicitly set this offset. The offset
can only be set early on, if no MMIO range has been mapped before.

With those, and the mesa MR at [1], I managed to run a 32-bit x86
glmark2 through FEX without using the host mesa (if we were to use
the thunked mesa lib, both the kernel and mesa would use
MMIO_OFFSET_64BIT, and the problem doesn't exist anymore).

Regards,

Boris

Changes in v2:
- Simplify the logic in patch2 to have a lockless solution that's
  still safe for what we need

[1]https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34573

Boris Brezillon (2):
  drm/panthor: Add missing explicit padding in drm_panthor_gpu_info
  drm/panthor: Fix the user MMIO offset logic for emulators

 drivers/gpu/drm/panthor/panthor_device.h | 18 ++++++++
 drivers/gpu/drm/panthor/panthor_drv.c    | 56 +++++++++++++++++-------
 include/uapi/drm/panthor_drm.h           | 41 +++++++++++++++++
 3 files changed, 99 insertions(+), 16 deletions(-)