[PATCH v3 1/5] x86: provide mb() macro

[Philip Oberfichtner]

Implement a x86 memory barrier mb(). Furthermore, remove the previously
used mfence() function, which does the same thing.

The mb() macro is now equivalent to Linux (v6.9):
linux/arch/x86/include/asm/barrier.h

Signed-off-by: Philip Oberfichtner <pro at denx.de>
---

Notes:
    Changes in V3:
    	- Remove mfence() function

 arch/x86/cpu/mp_init.c     | 10 +++++-----
 arch/x86/include/asm/cpu.h |  5 -----
 arch/x86/include/asm/io.h  |  1 +
 3 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/x86/cpu/mp_init.c b/arch/x86/cpu/mp_init.c
index aa1f47d7227..e2e1849c065 100644
--- a/arch/x86/cpu/mp_init.c
+++ b/arch/x86/cpu/mp_init.c
@@ -164,12 +164,12 @@ static inline void barrier_wait(atomic_t *b)
 {
 	while (atomic_read(b) == 0)
 		asm("pause");
-	mfence();
+	mb();
 }
 
 static inline void release_barrier(atomic_t *b)
 {
-	mfence();
+	mb();
 	atomic_set(b, 1);
 }
 
@@ -631,7 +631,7 @@ static int run_ap_work(struct mp_callback *callback, struct udevice *bsp,
 		if (cur_cpu != i)
 			store_callback(&ap_callbacks[i], callback);
 	}
-	mfence();
+	mb();
 
 	/* Wait for all the APs to signal back that call has been accepted. */
 	start = get_timer(0);
@@ -656,7 +656,7 @@ static int run_ap_work(struct mp_callback *callback, struct udevice *bsp,
 	} while (cpus_accepted != num_aps);
 
 	/* Make sure we can see any data written by the APs */
-	mfence();
+	mb();
 
 	return 0;
 }
@@ -692,7 +692,7 @@ static int ap_wait_for_instruction(struct udevice *cpu, void *unused)
 
 		/* Copy to local variable before using the value */
 		memcpy(&lcb, cb, sizeof(lcb));
-		mfence();
+		mb();
 		if (lcb.logical_cpu_number == MP_SELECT_ALL ||
 		    lcb.logical_cpu_number == MP_SELECT_APS ||
 		    dev_seq(cpu) == lcb.logical_cpu_number)
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 073f80b07f1..87e0c6f12b6 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -185,11 +185,6 @@ static inline int flag_is_changeable_p(uint32_t flag)
 }
 #endif
 
-static inline void mfence(void)
-{
-	__asm__ __volatile__("mfence" : : : "memory");
-}
-
 /**
  * cpu_enable_paging_pae() - Enable PAE-paging
  *
diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index c6d90eb794a..1390193f09c 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -240,6 +240,7 @@ static inline void sync(void)
  * have some advantages to use them instead of the simple one here.
  */
 #define dmb()		__asm__ __volatile__ ("" : : : "memory")
+#define mb()		__asm__ __volatile__ ("mfence" : : : "memory")
 #define __iormb()	dmb()
 #define __iowmb()	dmb()
 
-- 
2.39.2