[PATCH v2 17/17] drm/panthor: Add a debugfs knobs to simulate reset failures

[Boris Brezillon]

It's almost impossible to trigger a situation where the reset
doesn't work now that the driver is more mature, so let's add two
knobs to exercise this error path:

- a knob to trigger a reset
- a knob to fake an error in the reset path

Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panthor/panthor_device.c | 45 +++++++++++++++++++++++++++++++-
 drivers/gpu/drm/panthor/panthor_device.h |  8 ++++++
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
index 012edf5d590c..09c9cc922e70 100644
--- a/drivers/gpu/drm/panthor/panthor_device.c
+++ b/drivers/gpu/drm/panthor/panthor_device.c
@@ -198,7 +198,10 @@ static void panthor_device_reset_work(struct work_struct *work)
 	panthor_hw_soft_reset(ptdev);
 	panthor_hw_l2_power_on(ptdev);
 	panthor_mmu_post_reset(ptdev);
-	ret = panthor_fw_post_reset(ptdev);
+	if (ptdev->reset.fake_failure)
+		ret = -EIO;
+	else
+		ret = panthor_fw_post_reset(ptdev);
 	panthor_sched_post_reset(ptdev, ret != 0);
 	drm_dev_exit(cookie);
 
@@ -699,6 +702,40 @@ DEFINE_DEBUGFS_ATTRIBUTE(panthor_device_fake_unplug_failure_fops,
 			 panthor_device_fake_unplug_failure_get,
 			 panthor_device_fake_unplug_failure_set, "%llu\n");
 
+static int panthor_device_fake_fw_reset_failure_get(void *data, u64 *val)
+{
+	struct panthor_device *ptdev = data;
+
+	*val = ptdev->reset.fake_failure ? 1 : 0;
+	return 0;
+}
+
+static int panthor_device_fake_fw_reset_failure_set(void *data, u64 val)
+{
+	struct panthor_device *ptdev = data;
+
+	ptdev->reset.fake_failure = val ? true : false;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(panthor_device_fake_fw_reset_failure_fops,
+			 panthor_device_fake_fw_reset_failure_get,
+			 panthor_device_fake_fw_reset_failure_set, "%llu\n");
+
+static ssize_t panthor_device_reset_file_write(struct file *file,
+					       const char __user *, size_t size,
+					       loff_t *)
+{
+	struct panthor_device *ptdev = file_inode(file)->i_private;
+
+	panthor_device_schedule_reset(ptdev);
+	return size;
+}
+
+static const struct debugfs_short_fops panthor_device_reset_fops = {
+	.write = panthor_device_reset_file_write,
+};
+
 void panthor_device_debugfs_init(struct drm_minor *minor)
 {
 	struct panthor_device *ptdev = container_of(minor->dev, struct panthor_device, base);
@@ -706,6 +743,12 @@ void panthor_device_debugfs_init(struct drm_minor *minor)
 	debugfs_create_file("fake_unplug_failure", 0644,
 			    minor->debugfs_root, ptdev,
 			    &panthor_device_fake_unplug_failure_fops);
+	debugfs_create_file("fake_fw_reset_failure", 0644,
+			    minor->debugfs_root, ptdev,
+			    &panthor_device_fake_fw_reset_failure_fops);
+	debugfs_create_file("reset", 0200,
+			    minor->debugfs_root, ptdev,
+			    &panthor_device_reset_fops);
 	panthor_mmu_debugfs_init(minor);
 	panthor_gem_debugfs_init(minor);
 }
diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
index b2788373bfa9..160593824ef2 100644
--- a/drivers/gpu/drm/panthor/panthor_device.h
+++ b/drivers/gpu/drm/panthor/panthor_device.h
@@ -313,6 +313,14 @@ struct panthor_device {
 		 * all FW sections to make sure we start from a fresh state.
 		 */
 		bool fast;
+
+		/**
+		 * @fake_failure: When true, pretend the FW boot in the reset path failed.
+		 *
+		 * This is important to check that we're doing the right thing in this very
+		 * unlikely case.
+		 */
+		bool fake_failure;
 	} reset;
 
 	/** @pm: Power management related data. */

-- 
2.55.0