linux-kernel - [PATCH v2 2/3] drm/i915/utils: do not depend on config being defined

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Date:   Wed, 29 Sep 2021 11:33:56 -0700
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     intel-gfx@...ts.freedesktop.org
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        dri-devel@...ts.freedesktop.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/3] drm/i915/utils: do not depend on config being defined

Like the IS_ENABLED() counterpart, we can make IS_CONFIG_NONZERO() to
return the right thing when the config is not defined rather than a
build error, with the limitation that it can't be used on preprocessor
context.

The trick here is that macro names can't start with a number or dash, so
we stringify the argument and check that the first char is a number != 0
(or starting with a dash to cover negative numbers). Except for -O0
builds the strings are all eliminated.

Taking CONFIG_DRM_I915_REQUEST_TIMEOUT in
drivers/gpu/drm/i915/gem/i915_gem_context.c as example, we have the
following output of the preprocessor:

old:
 if (((20000) != 0) &&
new:
 if (( ("20000"[0] > '0' && "20000"[0] < '9') || "20000"[0] == '-' ) &&

New one looks worse, but is also eliminated from the object:

$ size drivers/gpu/drm/i915/gem/i915_gem_context.o.*
   text    data     bss     dec     hex filename
  52021    1070     232   53323    d04b drivers/gpu/drm/i915/gem/i915_gem_context.o.new
  52021    1070     232   53323    d04b drivers/gpu/drm/i915/gem/i915_gem_context.o.old

Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
---
 drivers/gpu/drm/i915/i915_utils.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index 02bbfa4d68d3..436ce612c46a 100644
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -28,6 +28,7 @@
 #include <linux/list.h>
 #include <linux/overflow.h>
 #include <linux/sched.h>
+#include <linux/stringify.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
@@ -469,6 +470,9 @@ static inline bool timer_expired(const struct timer_list *t)
  *
  * Returns 0 if @config is 0, 1 if set to any value.
  */
-#define IS_CONFIG_NONZERO(config) ((config) != 0)
+#define IS_CONFIG_NONZERO(config) (						\
+	(__stringify_1(config)[0] > '0' && __stringify_1(config)[0] < '9') ||	\
+	__stringify_1(config)[0] == '-'						\
+)
 
 #endif /* !__I915_UTILS_H */
-- 
2.33.0