[PATCH 1/8] clocksource: timer-riscv: select CSR from device tree

[Antony Pavlov]

barebox timer-riscv driver supports one of user counters:

  * 'cycle', counter for RDCYCLE instruction (CSR 0xc00);
  * 'time', timer for RDTIME instruction (CSR 0xc01).

At the moment in M-mode timer-riscv uses the 'cycle' counter,
and in S-mode timer-riscv uses the 'time' timer.

Alas picorv32 CPU core supports only the 'cycle' counter.
VexRiscV CPU core in M-mode supports only the 'time' timer.

This patch makes it possible to use the 'time' timer
for VexRiscV CPU in M-mode.

See also http://lists.infradead.org/pipermail/barebox/2021-May/036067.html

Signed-off-by: Antony Pavlov <antonynpavlov at gmail.com>
---
 arch/riscv/dts/erizo.dtsi         |  2 ++
 drivers/clocksource/timer-riscv.c | 24 ++++++++++++------------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/dts/erizo.dtsi b/arch/riscv/dts/erizo.dtsi
index 228711bd69..4eb92ae6f1 100644
--- a/arch/riscv/dts/erizo.dtsi
+++ b/arch/riscv/dts/erizo.dtsi
@@ -22,6 +22,8 @@
 
 		timebase-frequency = <24000000>;
 
+		barebox,csr-cycle;
+
 		cpu at 0 {
 			device_type = "cpu";
 			compatible = "cliffordwolf,picorv32", "riscv";
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 5a517fe6b4..96637f988a 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -12,9 +12,8 @@
 #include <clock.h>
 #include <asm/timer.h>
 #include <asm/csr.h>
-#include <asm/system.h>
 
-static u64 notrace riscv_timer_get_count_sbi(void)
+static u64 notrace riscv_timer_get_count_time(void)
 {
 	__maybe_unused u32 hi, lo;
 
@@ -29,7 +28,7 @@ static u64 notrace riscv_timer_get_count_sbi(void)
 	return ((u64)hi << 32) | lo;
 }
 
-static u64 notrace riscv_timer_get_count_rdcycle(void)
+static u64 notrace riscv_timer_get_count_cycle(void)
 {
 	__maybe_unused u32 hi, lo;
 
@@ -44,24 +43,25 @@ static u64 notrace riscv_timer_get_count_rdcycle(void)
 	return ((u64)hi << 32) | lo;
 }
 
-static u64 notrace riscv_timer_get_count(void)
-{
-	if (riscv_mode() == RISCV_S_MODE)
-		return riscv_timer_get_count_sbi();
-	else
-		return riscv_timer_get_count_rdcycle();
-}
-
 static struct clocksource riscv_clocksource = {
-	.read		= riscv_timer_get_count,
 	.mask		= CLOCKSOURCE_MASK(64),
 	.priority	= 100,
 };
 
 static int riscv_timer_init(struct device_d* dev)
 {
+	struct device_node *cpu;
+
 	dev_dbg(dev, "running at %lu Hz\n", riscv_timebase);
 
+	cpu = of_find_node_by_path("/cpus");
+
+	if (of_property_read_bool(cpu, "barebox,csr-cycle")) {
+		riscv_clocksource.read = riscv_timer_get_count_cycle;
+	} else {
+		riscv_clocksource.read = riscv_timer_get_count_time;
+	}
+
 	riscv_clocksource.mult = clocksource_hz2mult(riscv_timebase, riscv_clocksource.shift);
 
 	return init_clock(&riscv_clocksource);
-- 
2.32.0