[PATCH v2 04/30] drm/xe/forcewake: Add scope-based cleanup for forcewake

[Matt Roper <matthew.d.roper@intel.com>]

Since forcewake uses a reference counting get/put model, there are many
places where we need to be careful to drop the forcewake reference when
bailing out of a function early on an error path.  Add scope-based
cleanup options that can be used in place of explicit get/put to help
prevent mistakes in this area.

Examples:

   CLASS(xe_force_wake, fw_ref)(gt_to_fw(gt), XE_FW_GT);

       Obtain forcewake on the XE_FW_GT domain and hold it until the
       end of the current block.  The wakeref will be dropped
       automatically when the current scope is exited by any means
       (return, break, reaching the end of the block, etc.).

   xe_with_force_wake(fw_ref, gt_to_fw(ss->gt), XE_FORCEWAKE_ALL) {
        ...
   }

       Hold all forcewake domains for the following block.  As with the
       CLASS usage, forcewake will be dropped automatically when the
       block is exited by any means.

Use of these cleanup helpers should allow us to remove some ugly
goto-based error handling and help avoid mistakes in functions with lots
of early error exits.

v2:
 - Create a separate constructor that just wraps xe_force_wake_get for
   use in the class.  This eliminates the need to update the signature
   of xe_force_wake_get().  (Michal)

Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
---
 drivers/gpu/drm/xe/xe_force_wake.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_force_wake.h b/drivers/gpu/drm/xe/xe_force_wake.h
index 0e3e84bfa51c..0204503b53a0 100644
--- a/drivers/gpu/drm/xe/xe_force_wake.h
+++ b/drivers/gpu/drm/xe/xe_force_wake.h
@@ -61,4 +61,32 @@ xe_force_wake_ref_has_domain(unsigned int fw_ref, enum xe_force_wake_domains dom
 	return fw_ref & domain;
 }
 
+struct xe_force_wake_ref {
+	struct xe_force_wake *fw;
+	unsigned int domains;
+};
+
+static struct xe_force_wake_ref
+xe_force_wake_constructor(struct xe_force_wake *fw, unsigned int domains)
+{
+	struct xe_force_wake_ref fw_ref = { .fw = fw };
+
+	fw_ref.domains = xe_force_wake_get(fw, domains);
+
+	return fw_ref;
+}
+
+DEFINE_CLASS(xe_force_wake, struct xe_force_wake_ref,
+	     xe_force_wake_put(_T.fw, _T.domains),
+	     xe_force_wake_constructor(fw, domains),
+	     struct xe_force_wake *fw, unsigned int domains);
+
+/*
+ * Scoped helper for the forcewake class, using the same trick as scoped_guard()
+ * to bind the lifetime to the next statement/block.
+ */
+#define xe_with_force_wake(ref, fw, domains) \
+	for (CLASS(xe_force_wake, ref)(fw, domains), *done = NULL; \
+	     !done; done = (void *)1)
+
 #endif
-- 
2.51.1