[PATCH v11 09/19] drm_print: add CONFIG_DRM_USE_DYNAMIC_DEBUG

[Jim Cromie]

DRM.debug API is used thousands of times in drivers/gpu/drm/*; when
these are implemented using dynamic-debug, DYNAMIC_DEBUG_METADATA adds
a struct _ddebug (56 bytes) per site.

Since i915 will have ~2k callsites, and amdgpu ~4k, the memory costs
are substantial, and thus made configurable.

For a baseline:
bash-5.1# drms_load
[   10.923093] dyndbg:   1 debug prints in module drm
[   10.928345] ACPI: bus type drm_connector registered
[   11.034012] dyndbg:   2 debug prints in module ttm
[   11.038188] dyndbg:   8 debug prints in module video
[   11.551064] dyndbg: 127 debug prints in module i915
[   11.617106] AMD-Vi: AMD IOMMUv2 functionality not available on this system - This is not a bug.
[   12.084856] dyndbg: 2196 debug prints in module amdgpu
[   12.099040] [drm] amdgpu kernel modesetting enabled.
[   12.099790] amdgpu: CRAT table not found
[   12.100523] amdgpu: Virtual CRAT table created for CPU
[   12.100901] amdgpu: Topology: Add CPU node
[   12.165382] dyndbg:   3 debug prints in module wmi
[   12.356424] dyndbg:   3 debug prints in module nouveau

i915/gvt has pr_debugs that show up here
amdgpu has many pr_debugs from macro expansions

Signed-off-by: Jim Cromie <jim.cromie at gmail.com>

fixup-mk
---
 drivers/gpu/drm/Kconfig  | 12 ++++++++++++
 drivers/gpu/drm/Makefile |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 0039df26854b..4e7b865c3441 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -62,6 +62,18 @@ config DRM_DEBUG_MM
 
 	  If in doubt, say "N".
 
+config DRM_USE_DYNAMIC_DEBUG
+	bool "use dynamic debug to implement drm.debug"
+	default y
+	depends on DRM
+	depends on DYNAMIC_DEBUG || DYNAMIC_DEBUG_CORE
+	depends on JUMP_LABEL
+	help
+	  Use dynamic-debug to avoid drm_debug_enabled() runtime overheads.
+	  Due to callsite counts in DRM drivers (~4k in amdgpu) and 56
+	  bytes per callsite, the .data costs can be substantial, and
+	  are therefore configurable.
+
 config DRM_DEBUG_SELFTEST
 	tristate "kselftests for DRM"
 	depends on DRM
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 0dff40bb863c..60f4d7bc27eb 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -3,6 +3,8 @@
 # Makefile for the drm device driver.  This driver provides support for the
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
 
+CFLAGS-$(CONFIG_DRM_USE_DYNAMIC_DEBUG)	+= -DDYNAMIC_DEBUG_MODULE
+
 drm-y       :=	drm_aperture.o drm_auth.o drm_cache.o \
 		drm_file.o drm_gem.o drm_ioctl.o drm_irq.o \
 		drm_drv.o \
-- 
2.33.1