Re: [PATCH v3 08/13] drm/xe/pat: Return error from xe_pat_init_early() on unknown platform

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 9/8/2026 12:45 PM, Dnyaneshwar Bhadane wrote:
> xe_pat_init_early() currently only logs an error when the platform's
> graphics version doesn't match any known PAT table, but continues
> probing with an uninitialized pat.ops. This can lead to a NULL
> pointer dereference later when pat.ops is used.
> 
> Change xe_pat_init_early() to return an int and propagate -ENODATA
> to xe_device_probe() so the driver fails to load cleanly instead of
> continuing in a broken state.
> 

Fixes: ??

> Signed-off-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_device.c |  4 +++-
>  drivers/gpu/drm/xe/xe_pat.c    | 14 +++++---------
>  drivers/gpu/drm/xe/xe_pat.h    |  2 +-
>  3 files changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> index 8583b2e9ecf4..b7f78d45dee1 100644
> --- a/drivers/gpu/drm/xe/xe_device.c
> +++ b/drivers/gpu/drm/xe/xe_device.c
> @@ -960,7 +960,9 @@ int xe_device_probe(struct xe_device *xe)
>  	int err;
>  	u8 id;
>  
> -	xe_pat_init_early(xe);
> +	err = xe_pat_init_early(xe);
> +	if (err)
> +		return err;
>  
>  	err = xe_sriov_init(xe);
>  	if (err)
> diff --git a/drivers/gpu/drm/xe/xe_pat.c b/drivers/gpu/drm/xe/xe_pat.c
> index a5fe1beec652..8af92e3c4c17 100644
> --- a/drivers/gpu/drm/xe/xe_pat.c
> +++ b/drivers/gpu/drm/xe/xe_pat.c
> @@ -590,7 +590,7 @@ static const struct xe_pat_ops xe3p_xpc_pat_ops = {
>  	.entry_dump = xe3p_xpc_pat_entry_dump,
>  };
>  

now it's time to add kernel-doc
> -void xe_pat_init_early(struct xe_device *xe)
> +int xe_pat_init_early(struct xe_device *xe)
>  {
>  	xe->pat.idx[XE_CACHE_WB_COMPRESSION] = XE_PAT_INVALID_IDX;
>  	xe->pat.idx[XE_CACHE_NONE_COMPRESSION] = XE_PAT_INVALID_IDX;
> @@ -678,22 +678,18 @@ void xe_pat_init_early(struct xe_device *xe)
>  		xe->pat.idx[XE_CACHE_WT] = 2;
>  		xe->pat.idx[XE_CACHE_WB] = 0;
>  	} else {
> -		/*
> -		 * Going forward we expect to need new PAT settings for most
> -		 * new platforms; failure to provide a new table can easily
> -		 * lead to subtle, hard-to-debug problems.  If none of the
> -		 * conditions above match the platform we're running on we'll
> -		 * raise an error rather than trying to silently inherit the
> -		 * most recent platform's behavior.
> -		 */

can't we leave this comment as-is?

>  		drm_err(&xe->drm, "Missing PAT table for platform with graphics version %d.%02d!\n",
>  			GRAPHICS_VER(xe), GRAPHICS_VERx100(xe) % 100);
> +		return -ENODATA;
> +
>  	}
>  
> +	xe_assert(xe, xe->pat.ops);
>  	xe_assert(xe, xe->pat.ops->dump);
>  	xe_assert(xe, xe->pat.ops->program_graphics);
>  	xe_assert(xe, MEDIA_VER(xe) < 13 || xe->pat.ops->program_media);
>  	xe_assert(xe, GRAPHICS_VER(xe) < 20 || xe->pat.ops->entry_dump);
> +	return 0;
>  }
>  
>  void xe_pat_init(struct xe_gt *gt)
> diff --git a/drivers/gpu/drm/xe/xe_pat.h b/drivers/gpu/drm/xe/xe_pat.h
> index 7060f66e1d63..66e335fb3b0c 100644
> --- a/drivers/gpu/drm/xe/xe_pat.h
> +++ b/drivers/gpu/drm/xe/xe_pat.h
> @@ -43,7 +43,7 @@ struct xe_pat_table_entry {
>   * xe_pat_init_early - SW initialization, setting up data based on device
>   * @xe: xe device
>   */
> -void xe_pat_init_early(struct xe_device *xe);
> +int xe_pat_init_early(struct xe_device *xe);
>  
>  /**
>   * xe_pat_init - Program HW PAT table