[PATCH 13/20] riscv: add support for MMIO access to the timer registers

[Christoph Hellwig]

When running in M-mode we can't use the SBI to set the timer, and
don't have access to the time CSR as that usually is emulated by
M-mode.  Instead provide code that directly accesses the MMIO for
the timer.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 arch/riscv/include/asm/sbi.h      |  3 ++-
 arch/riscv/include/asm/timex.h    | 19 +++++++++++++++++--
 drivers/clocksource/timer-riscv.c | 21 +++++++++++++++++----
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 0cb74eccc73f..a4774bafe033 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -95,7 +95,8 @@ static inline void sbi_remote_sfence_vma_asid(const unsigned long *hart_mask,
 	SBI_CALL_4(SBI_REMOTE_SFENCE_VMA_ASID, hart_mask, start, size, asid);
 }
 #else /* CONFIG_RISCV_SBI */
-/* stub to for code is only reachable under IS_ENABLED(CONFIG_RISCV_SBI): */
+/* stubs to for code is only reachable under IS_ENABLED(CONFIG_RISCV_SBI): */
+void sbi_set_timer(uint64_t stime_value);
 void sbi_remote_fence_i(const unsigned long *hart_mask);
 #endif /* CONFIG_RISCV_SBI */
 #endif /* _ASM_RISCV_SBI_H */
diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index c7ef131b9e4c..e17837d61667 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -7,12 +7,25 @@
 #define _ASM_RISCV_TIMEX_H
 
 #include <asm/csr.h>
+#include <asm/io.h>
 
 typedef unsigned long cycles_t;
 
+extern u64 __iomem *riscv_time_val;
+extern u64 __iomem *riscv_time_cmp;
+
+#ifdef CONFIG_64BIT
+#define mmio_get_cycles()	readq_relaxed(riscv_time_val)
+#else
+#define mmio_get_cycles()	readl_relaxed(riscv_time_val)
+#define mmio_get_cycles_hi()	readl_relaxed(((u32 *)riscv_time_val) + 1)
+#endif
+
 static inline cycles_t get_cycles(void)
 {
-	return csr_read(CSR_TIME);
+	if (IS_ENABLED(CONFIG_RISCV_SBI))
+		return csr_read(CSR_TIME);
+	return mmio_get_cycles();
 }
 #define get_cycles get_cycles
 
@@ -24,7 +37,9 @@ static inline u64 get_cycles64(void)
 #else /* CONFIG_64BIT */
 static inline u32 get_cycles_hi(void)
 {
-	return csr_read(CSR_TIMEH);
+	if (IS_ENABLED(CONFIG_RISCV_SBI))
+		return csr_read(CSR_TIMEH);
+	return mmio_get_cycles_hi();
 }
 
 static inline u64 get_cycles64(void)
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 5d2fdc3e28a9..2b9fbc4ebe49 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -3,9 +3,9 @@
  * 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.
+ * All RISC-V systems have a timer attached to every hart.  These timers can
+ * either be read from the "time" and "timeh" CSRs, and can use the SBI to
+ * setup events, or directly accessed using MMIO registers.
  */
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
@@ -13,14 +13,27 @@
 #include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/sched_clock.h>
+#include <linux/io-64-nonatomic-lo-hi.h>
 #include <asm/smp.h>
 #include <asm/sbi.h>
 
+u64 __iomem *riscv_time_cmp;
+u64 __iomem *riscv_time_val;
+
+static inline void mmio_set_timer(u64 val)
+{
+	writeq_relaxed(val,
+		riscv_time_cmp + cpuid_to_hartid_map(smp_processor_id()));
+}
+
 static int riscv_clock_next_event(unsigned long delta,
 		struct clock_event_device *ce)
 {
 	csr_set(CSR_XIE, XIE_XTIE);
-	sbi_set_timer(get_cycles64() + delta);
+	if (IS_ENABLED(CONFIG_RISCV_SBI))
+		sbi_set_timer(get_cycles64() + delta);
+	else
+		mmio_set_timer(get_cycles64() + delta);
 	return 0;
 }
 
-- 
2.20.1