linux-kernel - [PATCH 06/20] riscv: don't use the rdtime(h) pseudo-instructions

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Date:   Tue,  3 Sep 2019 11:32:25 +0200
From:   Christoph Hellwig <hch@....de>
To:     Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Damien Le Moal <damien.lemoal@....com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Atish Patra <atish.patra@....com>
Subject: [PATCH 06/20] riscv: don't use the rdtime(h) pseudo-instructions

If we just use the CSRs that these map to directly the code is simpler
and doesn't require extra inline assembly code.  Also fix up the top-level
comment in timer-riscv.c to not talk about the cycle count or mention
details of the clocksource interface, of which this file is just a
consumer.

Signed-off-by: Christoph Hellwig <hch@....de>
Reviewed-by: Atish Patra <atish.patra@....com>
---
 arch/riscv/include/asm/timex.h    | 44 +++++++++++++++----------------
 drivers/clocksource/timer-riscv.c | 17 +++---------
 2 files changed, 25 insertions(+), 36 deletions(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 6a703ec9d796..c7ef131b9e4c 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -6,43 +6,41 @@
 #ifndef _ASM_RISCV_TIMEX_H
 #define _ASM_RISCV_TIMEX_H
 
-#include <asm/param.h>
+#include <asm/csr.h>
 
 typedef unsigned long cycles_t;
 
-static inline cycles_t get_cycles_inline(void)
+static inline cycles_t get_cycles(void)
 {
-	cycles_t n;
-
-	__asm__ __volatile__ (
-		"rdtime %0"
-		: "=r" (n));
-	return n;
+	return csr_read(CSR_TIME);
 }
-#define get_cycles get_cycles_inline
+#define get_cycles get_cycles
 
 #ifdef CONFIG_64BIT
-static inline uint64_t get_cycles64(void)
+static inline u64 get_cycles64(void)
+{
+	return get_cycles();
+}
+#else /* CONFIG_64BIT */
+static inline u32 get_cycles_hi(void)
 {
-        return get_cycles();
+	return csr_read(CSR_TIMEH);
 }
-#else
-static inline uint64_t get_cycles64(void)
+
+static inline u64 get_cycles64(void)
 {
-	u32 lo, hi, tmp;
-	__asm__ __volatile__ (
-		"1:\n"
-		"rdtimeh %0\n"
-		"rdtime %1\n"
-		"rdtimeh %2\n"
-		"bne %0, %2, 1b"
-		: "=&r" (hi), "=&r" (lo), "=&r" (tmp));
+	u32 hi, lo;
+
+	do {
+		hi = get_cycles_hi();
+		lo = get_cycles();
+	} while (hi != get_cycles_hi());
+
 	return ((u64)hi << 32) | lo;
 }
-#endif
+#endif /* CONFIG_64BIT */
 
 #define ARCH_HAS_READ_CURRENT_TIMER
-
 static inline int read_current_timer(unsigned long *timer_val)
 {
 	*timer_val = get_cycles();
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 09e031176bc6..470c7ef02ea4 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -2,6 +2,10 @@
 /*
  * Copyright (C) 2012 Regents of the University of California
  * Copyright (C) 2017 SiFive
+ *
+ * All RISC-V systems have a timer attached to every hart.  These timers can be
+ * read from the "time" and "timeh" CSRs, and can use the SBI to setup
+ * events.
  */
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
@@ -12,19 +16,6 @@
 #include <asm/smp.h>
 #include <asm/sbi.h>
 
-/*
- * All RISC-V systems have a timer attached to every hart.  These timers can be
- * read by the 'rdcycle' pseudo instruction, and can use the SBI to setup
- * events.  In order to abstract the architecture-specific timer reading and
- * setting functions away from the clock event insertion code, we provide
- * function pointers to the clockevent subsystem that perform two basic
- * operations: rdtime() reads the timer on the current CPU, and
- * next_event(delta) sets the next timer event to 'delta' cycles in the future.
- * As the timers are inherently a per-cpu resource, these callbacks perform
- * operations on the current hart.  There is guaranteed to be exactly one timer
- * per hart on all RISC-V systems.
- */
-
 static int riscv_clock_next_event(unsigned long delta,
 		struct clock_event_device *ce)
 {
-- 
2.20.1