[PATCH] [RFC]drm/xe: Introduce active ccs tracking

[Lucas De Marchi]

On Fri, Sep 20, 2024 at 07:05:14PM GMT, Tejas Upadhyay wrote:
>Current ccs_mode setting is allowed when no client has
>actively opened device. Instead it should be restricted
> if there is any active ccs engine in use.
>
>Closing device fd is always a async and may lead to show
>client present even after fd is closed from user perspective.
>
>Signed-off-by: Tejas Upadhyay <tejas.upadhyay at intel.com>
>---
> drivers/gpu/drm/xe/xe_force_wake.c  | 3 +++
> drivers/gpu/drm/xe/xe_gt_ccs_mode.c | 8 ++++----
> drivers/gpu/drm/xe/xe_gt_types.h    | 6 ++++++
> 3 files changed, 13 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_force_wake.c b/drivers/gpu/drm/xe/xe_force_wake.c
>index a64c14757c84..51ab8e5dd583 100644
>--- a/drivers/gpu/drm/xe/xe_force_wake.c
>+++ b/drivers/gpu/drm/xe/xe_force_wake.c
>@@ -195,6 +195,9 @@ int xe_force_wake_put(struct xe_force_wake *fw,
> 		ret |= domain_sleep_wait(gt, domain);
> 	}
> 	fw->awake_domains &= ~sleep;
>+	if (!(fw->awake_domains & XE_FW_GT))
>+		if (gt->ccs_mode && !IS_SRIOV_VF(gt_to_xe(gt)))
>+			gt->ccs_active = 0;
> 	spin_unlock_irqrestore(&fw->lock, flags);
>
> 	return ret;
>diff --git a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>index 9360ac4de489..dbc49d595a6c 100644
>--- a/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>+++ b/drivers/gpu/drm/xe/xe_gt_ccs_mode.c
>@@ -69,6 +69,7 @@ static void __xe_gt_apply_ccs_mode(struct xe_gt *gt, u32 num_engines)
> 	}
>
> 	xe_mmio_write32(&gt->mmio, CCS_MODE, mode);
>+	gt->ccs_active = mode;
>
> 	xe_gt_dbg(gt, "CCS_MODE=%x config:%08x, num_engines:%d, num_slices:%d\n",
> 		  mode, config, num_engines, num_slices);
>@@ -132,10 +133,9 @@ ccs_mode_store(struct device *kdev, struct device_attribute *attr,
> 		return -EINVAL;
> 	}
>
>-	/* CCS mode can only be updated when there are no drm clients */
>-	spin_lock(&xe->clients.lock);
>-	if (xe->clients.count) {
>-		spin_unlock(&xe->clients.lock);
>+	/* CCS mode can only be updated when there is no active ccs_mode */

same question as before:  what happens if userspace cached the available
engines from a query (like it normally does) and then decide to submit
later?  CCS being idle doesn't mean we can change it. I think what we
really want is to track the userspace clients (i.e. ignore kernel
clients since those don't do anything with CCS, but probably add an
assert somewhere to guarantee it).

AFAIK it's not expected from umd point of view to have dynamic
changes on available engines. +Joonas, +Matthew Brost

Lucas De Marchi