drm/i915/guc: Speed up GuC log dumps

Add support for telling the debugfs interface the size of the GuC log
dump in advance. Without that, the underlying framework keeps calling
the 'show' function with larger and larger buffer allocations until it
fits. That means reading the log from graphics memory many times - 16
times with the full 18MB log size.

v2: Don't return error codes from size query. Report overflow in the
error dump as well (review feedback from Daniele).
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211211065859.2248188-2-John.C.Harrison@Intel.com

drivers/gpu/drm/i915/gt/intel_gt_debugfs.h

@@ -10,11 +10,7 @@
 
 struct intel_gt;
 
-#define DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(__name)				\
-	static int __name ## _open(struct inode *inode, struct file *file) \
-{									\
-	return single_open(file, __name ## _show, inode->i_private);	\
-}									\
+#define __GT_DEBUGFS_ATTRIBUTE_FOPS(__name)				\
 static const struct file_operations __name ## _fops = {			\
 	.owner = THIS_MODULE,						\
 	.open = __name ## _open,					\
@@ -23,6 +19,21 @@ static const struct file_operations __name ## _fops = {			\
 	.release = single_release,					\
 }
 
+#define DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(__name)			\
+static int __name ## _open(struct inode *inode, struct file *file)	\
+{									\
+	return single_open(file, __name ## _show, inode->i_private);	\
+}									\
+__GT_DEBUGFS_ATTRIBUTE_FOPS(__name)
+
+#define DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE_WITH_SIZE(__name, __size_vf)		\
+static int __name ## _open(struct inode *inode, struct file *file)		\
+{										\
+	return single_open_size(file, __name ## _show, inode->i_private,	\
+			    __size_vf(inode->i_private));			\
+}										\
+__GT_DEBUGFS_ATTRIBUTE_FOPS(__name)
+
 void intel_gt_debugfs_register(struct intel_gt *gt);
 
 struct intel_gt_debugfs_file {

drivers/gpu/drm/i915/gt/uc/intel_guc_log_debugfs.c

@@ -10,22 +10,74 @@
 #include "intel_guc.h"
 #include "intel_guc_log.h"
 #include "intel_guc_log_debugfs.h"
+#include "intel_uc.h"
+
+static u32 obj_to_guc_log_dump_size(struct drm_i915_gem_object *obj)
+{
+	u32 size;
+
+	if (!obj)
+		return PAGE_SIZE;
+
+	/* "0x%08x 0x%08x 0x%08x 0x%08x\n" => 16 bytes -> 44 chars => x2.75 */
+	size = ((obj->base.size * 11) + 3) / 4;
+
+	/* Add padding for final blank line, any extra header info, etc. */
+	size = PAGE_ALIGN(size + PAGE_SIZE);
+
+	return size;
+}
+
+static u32 guc_log_dump_size(struct intel_guc_log *log)
+{
+	struct intel_guc *guc = log_to_guc(log);
+
+	if (!intel_guc_is_supported(guc))
+		return PAGE_SIZE;
+
+	if (!log->vma)
+		return PAGE_SIZE;
+
+	return obj_to_guc_log_dump_size(log->vma->obj);
+}
 
 static int guc_log_dump_show(struct seq_file *m, void *data)
 {
 	struct drm_printer p = drm_seq_file_printer(m);
+	int ret;
 
-	return intel_guc_log_dump(m->private, &p, false);
+	ret = intel_guc_log_dump(m->private, &p, false);
+
+	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && seq_has_overflowed(m))
+		pr_warn_once("preallocated size:%zx for %s exceeded\n",
+			     m->size, __func__);
+
+	return ret;
+}
+DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE_WITH_SIZE(guc_log_dump, guc_log_dump_size);
+
+static u32 guc_load_err_dump_size(struct intel_guc_log *log)
+{
+	struct intel_guc *guc = log_to_guc(log);
+	struct intel_uc *uc = container_of(guc, struct intel_uc, guc);
+
+	if (!intel_guc_is_supported(guc))
+		return PAGE_SIZE;
+
+	return obj_to_guc_log_dump_size(uc->load_err_log);
 }
-DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(guc_log_dump);
 
 static int guc_load_err_log_dump_show(struct seq_file *m, void *data)
 {
 	struct drm_printer p = drm_seq_file_printer(m);
 
+	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && seq_has_overflowed(m))
+		pr_warn_once("preallocated size:%zx for %s exceeded\n",
+			     m->size, __func__);
+
 	return intel_guc_log_dump(m->private, &p, true);
 }
-DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(guc_load_err_log_dump);
+DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE_WITH_SIZE(guc_load_err_log_dump, guc_load_err_dump_size);
 
 static int guc_log_level_get(void *data, u64 *val)
 {