Re: [PATCH i-g-t] lib/intel_pat: add hardcoded PAT fallback for older kernels

[Matthew Auld <matthew.auld@intel.com>]

On 27/03/2026 05:22, himanshu.girotra@intel.com wrote:
> From: Himanshu Girotra <himanshu.girotra@intel.com>
> 
> When IGT runs on kernels that lack the gt0/pat_sw_config debugfs entry
> (commit "drm/xe: expose PAT software config to debugfs"), the PAT cache
> is NULL and intel_get_pat_idx() hits a fatal assertion.  This breaks
> basic tests like xe_exec_basic on stock distro kernels (e.g. Ubuntu
> 25.10).
> 
> Add xe_pat_fallback() with hardcoded PAT indices matching the kernel's
> xe_pat_init_early() for platforms up to Crescent Island (xe3p XPC).
> When the debugfs is unavailable, the fallback provides correct values
> instead of crashing.  Newer platforms (xe3p LPG and beyond) are not
> covered because their kernel support arrived after the debugfs entry
> was already in place.
> 
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Cc: Francois Dugast <francois.dugast@intel.com>
> Signed-off-by: Himanshu Girotra <himanshu.girotra@intel.com>

Reviewed-by: Matthew Auld <matthew.auld@intel.com>