linux-kernel - [PATCH 1/1] sh: add support for cmpxchg on u8 and u16 pointers

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Date:   Tue, 18 Aug 2020 23:05:11 -0400
From:   Liam Beguin <liambeguin@...il.com>
To:     liambeguin@...il.com, ysato@...rs.sourceforge.jp, dalias@...c.org
Cc:     linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: [PATCH 1/1] sh: add support for cmpxchg on u8 and u16 pointers

The kernel test bot reported[1] that using set_mask_bits on a u8 causes
the following issue on SuperH:

    >> ERROR: modpost: "__cmpxchg_called_with_bad_pointer" [drivers/phy/ti/phy-tusb1210.ko] undefined!

Add support for cmpxchg on u8 and u16 pointers.

[1] https://lore.kernel.org/patchwork/patch/1288894/#1485536

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Liam Beguin <liambeguin@...il.com>
---

Hi,

This was reported by the kernel test bot on an architecture I can't
really test on. I was only able to make sure the build succeeds, but
nothing more.
This patch is based on the __cmpxchg_u32 impletmentation and seems
incomplete based on the different cmpxchg headers I can find.

Do these function need to be impletmented in each header
simulataneously?

Thanks,
Liam

 arch/sh/include/asm/cmpxchg-irq.h | 27 +++++++++++++++++++++++++++
 arch/sh/include/asm/cmpxchg.h     |  5 +++--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/arch/sh/include/asm/cmpxchg-irq.h b/arch/sh/include/asm/cmpxchg-irq.h
index 07d3e7f08389..918c4153a930 100644
--- a/arch/sh/include/asm/cmpxchg-irq.h
+++ b/arch/sh/include/asm/cmpxchg-irq.h
@@ -51,4 +51,31 @@ static inline unsigned long __cmpxchg_u32(volatile int *m, unsigned long old,
 	return retval;
 }
 
+static inline unsigned long __cmpxchg_u16(volatile u16 *m, unsigned long old,
+	unsigned long new)
+{
+	u16 retval;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	retval = *m;
+	if (retval == old)
+		*m = new;
+	local_irq_restore(flags);
+	return (unsigned long)retval;
+}
+
+static inline unsigned long __cmpxchg_u8(volatile u8 *m, unsigned long old,
+	unsigned long new)
+{
+	u8 retval;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	retval = *m;
+	if (retval == old)
+		*m = new;
+	local_irq_restore(flags);
+	return (unsigned long)retval;
+}
 #endif /* __ASM_SH_CMPXCHG_IRQ_H */
diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
index e9501d85c278..7d65d0fd1665 100644
--- a/arch/sh/include/asm/cmpxchg.h
+++ b/arch/sh/include/asm/cmpxchg.h
@@ -56,8 +56,9 @@ static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old,
 		unsigned long new, int size)
 {
 	switch (size) {
-	case 4:
-		return __cmpxchg_u32(ptr, old, new);
+	case 4: return __cmpxchg_u32((int *)ptr, old, new);
+	case 2: return __cmpxchg_u16((u16 *)ptr, old, new);
+	case 1: return __cmpxchg_u8((u8 *)ptr, old, new);
 	}
 	__cmpxchg_called_with_bad_pointer();
 	return old;
-- 
2.27.0