Re: [PATCH 6/6] drm/xe/xe_guc_ct: Justify WRITE_ONCE/READ_ONCE usage

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Dec 18, 2025 at 03:35:34PM +0000, Jonathan Cavitt wrote:
> Usage of READ_ONCE and WRITE_ONCE requires comments justifying it.
> Some recently added uses had cross-dependencies with each other, but
> needed to be added separately, so introduce the justifications now when
> it makes more sense to.
> 
> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

No, I did not suggest that.

for instance below:

> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_guc_ct.c | 5 +++++
>  drivers/gpu/drm/xe/xe_guc_ct.h | 2 ++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> index 20ac0438ffb6..24857c2c8cb5 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> @@ -529,6 +529,11 @@ static void guc_ct_change_state(struct xe_guc_ct *ct,
>  	if (ct->g2h_outstanding)
>  		xe_pm_runtime_put(ct_to_xe(ct));
>  	ct->g2h_outstanding = 0;
> +
> +	/*
> +	 * WRITE_ONCE pairs with READ_ONCEs in xe_guc_ct_initialized and
> +	 * xe_guc_ct_enabled.
> +	 */


if this is true, then the patch 3 and 4 and this line should be combined in a single
fix and the only Fixes tag being the last patch, which introduced the relationship.
To the first patch that introduced the write without the need for the WRITE_ONCE.

>  	WRITE_ONCE(ct->state, state);
>  
>  	xe_gt_dbg(gt, "GuC CT communication channel %s\n",
> diff --git a/drivers/gpu/drm/xe/xe_guc_ct.h b/drivers/gpu/drm/xe/xe_guc_ct.h
> index cb1335f1d66f..8d318b094f33 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ct.h
> +++ b/drivers/gpu/drm/xe/xe_guc_ct.h
> @@ -30,11 +30,13 @@ void xe_guc_ct_print(struct xe_guc_ct *ct, struct drm_printer *p, bool want_ctb)
>  
>  static inline bool xe_guc_ct_initialized(struct xe_guc_ct *ct)
>  {
> +	/* READ_ONCE pairs with WRITE_ONCE in guc_ct_change_state */
>  	return READ_ONCE(ct->state) != XE_GUC_CT_STATE_NOT_INITIALIZED;
>  }
>  
>  static inline bool xe_guc_ct_enabled(struct xe_guc_ct *ct)
>  {
> +	/* READ_ONCE pairs with WRITE_ONCE in guc_ct_change_state */
>  	return READ_ONCE(ct->state) == XE_GUC_CT_STATE_ENABLED;
>  }
>  
> -- 
> 2.43.0
>