Re: [PATCH 06/12] riscv: add support for MMIO access to the timer registers

Paul Walmsley
2019-11-17T23:06:49Z

On Mon, 28 Oct 2019, Christoph Hellwig wrote:

> 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@lst.de>
> Reviewed-by: Anup Patel <anup@brainfault.org>

Thanks, queued the following for v5.5-rc1.

- Paul

From: Christoph Hellwig <hch@lst.de>
Date: Mon, 28 Oct 2019 13:10:37 +0100
Subject: [PATCH] riscv: add support for MMIO access to the timer registers

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@lst.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
[paul.walmsley@sifive.com: updated to apply; fixed checkpatch
issue; timex.h now includes asm/mmio.h to resolve header file
problems]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
---
arch/riscv/include/asm/sbi.h | 3 ++-
arch/riscv/include/asm/timex.h | 19 +++++++++++++++++--
drivers/clocksource/timer-riscv.c | 23 +++++++++++++++++++----
3 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 204af718df61..8e14d4819d0f 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 for code that is only reachable under IS_ENABLED(CONFIG_RISCV_SBI): */
+/* stubs for code that 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..bad2a7c2cda5 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/mmio.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 d083bfb535f6..4e54856ce2a5 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 +13,29 @@
#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)
+{
+ void __iomem *r;
+
+ r = riscv_time_cmp + cpuid_to_hartid_map(smp_processor_id());
+ writeq_relaxed(val, r);
+}
+
static int riscv_clock_next_event(unsigned long delta,
struct clock_event_device *ce)
{
csr_set(CSR_IE, IE_TIE);
- 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;
}

--
2.24.0.rc0