[PATCH 2/2] drm/xe: make change ccs_mode a synchronous action

[Lucas De Marchi]

On Mon, Dec 09, 2024 at 03:12:10PM +0100, Maciej Patelczyk wrote:
>If ccs_mode is being modified via
>   /sys/class/drm/cardX/device/tileY/gtY/ccs_mode
>the asynchronous reset is triggered and the write returns immediately.
>
>With that some test receive false information about number of CCS engines
>or even fail if they proceed without delay after changing the ccs_mode.
>
>Changing the ccs_mode change from async to sync to prevent failures in
>tests.
>
>Signed-off-by: Maciej Patelczyk <maciej.patelczyk at intel.com>
>---
> drivers/gpu/drm/xe/xe_gt_ccs_mode.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>index b6adfb9f2030..8d02ec3f7d12 100644
>--- a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>+++ b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>@@ -115,7 +115,7 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
> 	struct xe_gt *gt = kobj_to_gt(&kdev->kobj);
> 	struct xe_device *xe = gt_to_xe(gt);
> 	u32 num_engines, num_slices;
>-	int ret;
>+	int mode_changed = 0, ret;
>
> 	if (IS_SRIOV(xe)) {
> 		xe_gt_dbg(gt, "Can't change compute mode when running as %s\n",
>@@ -151,10 +151,14 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
> 		gt->ccs_mode = num_engines;
> 		xe_gt_record_user_engines(gt);
> 		xe_gt_reset_async(gt);
>+		mode_changed = 1;

I think this can simply be the sync version. We don't want to allow new
clients being created while this reset is taking place, which is what
the mutex below is protecting against. 

Lucas De Marchi

> 	}
>
> 	mutex_unlock(&xe->drm.filelist_mutex);
>
>+	if (mode_changed)
>+		xe_gt_reset_wait(gt);
>+
> 	return count;
> }
>
>-- 
>2.43.0
>