[PATCH v3 15/15] drm/i915/gt: Allow the user to change the CCS mode through sysfs

[Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>]

Create the 'ccs_mode' file under

/sys/class/drm/cardX/gt/gt0/ccs_mode

This file allows the user to read and set the current CCS mode.

 - Reading: The user can read the current CCS mode, which can be
   1, 2, or 4. This value is derived from the current engine
   mask.

 - Writing: The user can set the CCS mode to 1, 2, or 4,
   depending on the desired number of exposed engines and the
   required load balancing.

The interface will return -EBUSY if other clients are connected
to i915, or -EINVAL if an invalid value is set.

Signed-off-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c | 82 ++++++++++++++++++++-
 1 file changed, 80 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c b/drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c
index cc46ee9dea3f..1ed6153ff8cf 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_ccs_mode.c
@@ -6,6 +6,7 @@
 #include "i915_drv.h"
 #include "intel_engine_user.h"
 #include "intel_gt_ccs_mode.h"
+#include "intel_gt_pm.h"
 #include "intel_gt_print.h"
 #include "intel_gt_regs.h"
 #include "intel_gt_sysfs.h"
@@ -172,7 +173,7 @@ static int rb_engine_cmp(struct rb_node *rb_new, const struct rb_node *rb_old)
 	return new->uabi_class - old->uabi_class;
 }
 
-static void __maybe_unused add_uabi_ccs_engines(struct intel_gt *gt, u32 ccs_mode)
+static void add_uabi_ccs_engines(struct intel_gt *gt, u32 ccs_mode)
 {
 	struct drm_i915_private *i915 = gt->i915;
 	intel_engine_mask_t new_ccs_mask, tmp;
@@ -230,7 +231,7 @@ static void __maybe_unused add_uabi_ccs_engines(struct intel_gt *gt, u32 ccs_mod
 	mutex_unlock(&i915->uabi_engines_mutex);
 }
 
-static void __maybe_unused remove_uabi_ccs_engines(struct intel_gt *gt, u8 ccs_mode)
+static void remove_uabi_ccs_engines(struct intel_gt *gt, u8 ccs_mode)
 {
 	struct drm_i915_private *i915 = gt->i915;
 	intel_engine_mask_t new_ccs_mask, tmp;
@@ -273,8 +274,85 @@ static ssize_t num_cslices_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(num_cslices);
 
+static ssize_t ccs_mode_show(struct device *dev,
+			     struct device_attribute *attr, char *buff)
+{
+	struct intel_gt *gt = kobj_to_gt(&dev->kobj);
+	u32 ccs_mode;
+
+	ccs_mode = hweight32(gt->ccs.id_mask);
+
+	return sysfs_emit(buff, "%u\n", ccs_mode);
+}
+
+static ssize_t ccs_mode_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buff, size_t count)
+{
+	struct intel_gt *gt = kobj_to_gt(&dev->kobj);
+	int num_cslices = hweight32(CCS_MASK(gt));
+	int ccs_mode = hweight32(gt->ccs.id_mask);
+	ssize_t ret;
+	u32 val;
+
+	ret = kstrtou32(buff, 0, &val);
+	if (ret)
+		return ret;
+
+	/*
+	 * As of now possible values to be set are 1, 2, 4,
+	 * up to the maximum number of available slices
+	 */
+	if (!val || val > num_cslices || (num_cslices % val))
+		return -EINVAL;
+
+	/* Let's wait until the GT is no longer in use */
+	ret = intel_gt_pm_wait_for_idle(gt);
+	if (ret)
+		return ret;
+
+	mutex_lock(&gt->wakeref.mutex);
+
+	/*
+	 * Let's check again that the GT is idle,
+	 * we don't want to change the CCS mode
+	 * while someone is using the GT
+	 */
+	if (intel_gt_pm_is_awake(gt)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	/*
+	 * Nothing to do if the requested setting
+	 * is the same as the current one
+	 */
+	if (val == ccs_mode)
+		goto out;
+	else if (val > ccs_mode)
+		add_uabi_ccs_engines(gt, val);
+	else
+		remove_uabi_ccs_engines(gt, val);
+
+out:
+	mutex_unlock(&gt->wakeref.mutex);
+
+	return ret ?: count;
+}
+static DEVICE_ATTR_RW(ccs_mode);
+
 void intel_gt_sysfs_ccs_init(struct intel_gt *gt)
 {
 	if (sysfs_create_file(&gt->sysfs_gt, &dev_attr_num_cslices.attr))
 		gt_warn(gt, "Failed to create sysfs num_cslices files\n");
+
+	/*
+	 * Do not create the ccs_mode file for non DG2 platforms
+	 * because they don't need it as they have only one CCS engine
+	 */
+	if (!IS_DG2(gt->i915))
+		return;
+
+	if (sysfs_create_file(&gt->sysfs_gt, &dev_attr_ccs_mode.attr))
+		gt_warn(gt, "Failed to create sysfs ccs_mode files\n");
 }
-- 
2.45.2