drm/xe: Don't check BIOS-disabled FlatCCS if primary GT is disabled

If the primary is GT is disabled via configfs, we can't read the GT
registers that would tell us whether the BIOS has disabled FlatCCS on a
platform that would otherwise have it; we'll just proceed as if the
FlatCCS is still enabled.  This is similar to the situation seen by
SRIOV VFs and doesn't cause any functional problems since the hardware
will simply drop writes to the CCS region and reads will always come
back as 0 (indicating uncompressed data).  We'll simply miss out on the
chance to avoid some unnecessary overhead during BO creation and
migration.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-45-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index e2aa79a78938950373f18c4eae7082fd1c226564..5f6a412b571c79bc911d9a66b0d91c0fadd922f6 100644 (file)
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -782,6 +782,8 @@ static int probe_has_flat_ccs(struct xe_device *xe)
                return 0;
 
        gt = xe_root_mmio_gt(xe);
+       if (!gt)
+               return 0;
 
        fw_ref = xe_force_wake_get(gt_to_fw(gt), XE_FW_GT);
        if (!fw_ref)