linux-kernel - [PATCH] pmdomain: airoha: Fix compilation error with Clang-20 and Thumb2 mode

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Message-ID: <20250120153817.11807-1-ansuelsmth@gmail.com>
Date: Mon, 20 Jan 2025 16:38:09 +0100
From: Christian Marangi <ansuelsmth@...il.com>
To: Ulf Hansson <ulf.hansson@...aro.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Christian Marangi <ansuelsmth@...il.com>,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org,
	llvm@...ts.linux.dev
Cc: Sudeep Holla <sudeep.holla@....com>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH] pmdomain: airoha: Fix compilation error with Clang-20 and Thumb2 mode

The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame
pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling
hooks are inserted via the -pg switch.

This is a known issue and similar driver workaround this with a Makefile
ifdef. Exact workaround are applied in
drivers/firmware/arm_scmi/transports/Makefile and other similar driver.

Suggested-by: Sudeep Holla <sudeep.holla@....com>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501201840.XmpHXpQ4-lkp@intel.com/
Fixes: 82e703dd438b ("pmdomain: airoha: Add Airoha CPU PM Domain support")
Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
---
 drivers/pmdomain/mediatek/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pmdomain/mediatek/Makefile b/drivers/pmdomain/mediatek/Makefile
index 0f6edce9239b..18ba92e3c418 100644
--- a/drivers/pmdomain/mediatek/Makefile
+++ b/drivers/pmdomain/mediatek/Makefile
@@ -2,3 +2,10 @@
 obj-$(CONFIG_MTK_SCPSYS)		+= mtk-scpsys.o
 obj-$(CONFIG_MTK_SCPSYS_PM_DOMAINS) 	+= mtk-pm-domains.o
 obj-$(CONFIG_AIROHA_CPU_PM_DOMAIN) 	+= airoha-cpu-pmdomain.o
+
+ifeq ($(CONFIG_THUMB2_KERNEL)$(CONFIG_CC_IS_CLANG),yy)
+# The use of R7 in the SMCCC conflicts with the compiler's use of R7 as a frame
+# pointer in Thumb2 mode, which is forcibly enabled by Clang when profiling
+# hooks are inserted via the -pg switch.
+CFLAGS_REMOVE_airoha-cpu-pmdomain.o += $(CC_FLAGS_FTRACE)
+endif
-- 
2.47.1