Re: [PATCH v2 i-g-t] lib/intel_pat: Cache PAT config for unprivileged processes

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Thu, 05 Mar 2026 04:25:48 -0800, <himanshu.girotra@intel.com> wrote:
>
> diff --git a/lib/intel_pat.c b/lib/intel_pat.c
> index 8660a2515..1dcb84cc6 100644
> --- a/lib/intel_pat.c
> +++ b/lib/intel_pat.c
> @@ -6,6 +6,7 @@
>  #include <fcntl.h>
>  #include "igt.h"
>  #include "intel_pat.h"
> +#include "xe/xe_query.h"
>
>  /**
>   * xe_get_pat_sw_config - Helper to read PAT (Page Attribute Table) software configuration
> @@ -99,17 +100,18 @@ static void intel_get_pat_idx(int fd, struct intel_pat_cache *pat)
>	uint16_t dev_id;
>
>	/*
> -	 * For Xe driver, query the kernel's PAT software configuration
> -	 * via debugfs. The kernel is the authoritative source for PAT
> -	 * indices, accounting for platform-specific workarounds
> -	 * (e.g. Wa_16023588340) at runtime.
> +	 * For Xe, use the PAT cache stored in struct xe_device.
> +	 * xe_device_get() populates the cache while still root; forked
> +	 * children that inherit the xe_device can use it post-drop_root().
>	 */
>	if (is_xe_device(fd)) {
> -		int32_t parsed = xe_get_pat_sw_config(fd, pat);
> +		struct xe_device *xe_dev = xe_device_get(fd);
>
> -		igt_assert_f(parsed > 0,
> -			     "Failed to get PAT sw_config from debugfs (parsed=%d)\n",
> -			     parsed);
> +		igt_assert_f(xe_dev->pat_cached,
> +			     "PAT not cached in xe_device for fd %d -- "
> +			     "was xe_device_get() called before igt_drop_root()?\n",
> +			     fd);

Maybe change this print too since we are doing xe_device_get() right above.

> +		*pat = xe_dev->pat_cache;
>		return;
>	}
>