riscv: Rework riscv timer driver to only support S-mode

The riscv-timer driver currently serves as a shim for several riscv timer
drivers. This is not too desirable because it bypasses the usual timer
selection via the driver model. There is no easy way to specify an
alternate timing driver, or have the tick rate depend on the cpu's
configured frequency. The timer drivers also do not have device structs,
and so have to rely on storing parameters in gd_t. Lastly, there is no
initialization call, so driver init is done in the same function which
reads the time. This can result in confusing error messages. To a user, it
looks like the driver failed when trying to read the time, whereas it may
have failed while initializing.

This patch removes the shim functionality from the riscv-timer driver, and
has it instead implement the former rdtime.c timer driver. This is because
existing u-boot users who pass in a device tree (e.g. qemu) do not create a
timer device for S-mode u-boot. The existing behavior of creating the
riscv-timer device in the riscv cpu driver must be kept. The actual reading
of the CSRs has been redone in the style of Linux's get_cycles64.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Rick Chen <rick@andestech.com>

6 files changed, 3 insertions, 50 deletions

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 009a545fcf..21e6690f4d 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -185,14 +185,6 @@ config ANDES_PLMT
 	  The Andes PLMT block holds memory-mapped mtime register
 	  associated with timer tick.
 
-config RISCV_RDTIME
-	bool
-	default y if RISCV_SMODE || SPL_RISCV_SMODE
-	help
-	  The provides the riscv_get_time() API that is implemented using the
-	  standard rdtime instruction. This is the case for S-mode U-Boot, and
-	  is useful for processors that support rdtime in M-mode too.
-
 config SYS_MALLOC_F_LEN
 	default 0x1000
 
diff --git a/arch/riscv/cpu/ax25/Kconfig b/arch/riscv/cpu/ax25/Kconfig
index 8d8d71dcbf..5cb5bb51eb 100644
--- a/arch/riscv/cpu/ax25/Kconfig
+++ b/arch/riscv/cpu/ax25/Kconfig
@@ -3,7 +3,7 @@ config RISCV_NDS
 	select ARCH_EARLY_INIT_R
 	imply CPU
 	imply CPU_RISCV
-	imply RISCV_TIMER
+	imply RISCV_TIMER if (RISCV_SMODE || SPL_RISCV_SMODE)
 	imply ANDES_PLIC if (RISCV_MMODE || SPL_RISCV_MMODE)
 	imply ANDES_PLMT if (RISCV_MMODE || SPL_RISCV_MMODE)
 	imply SPL_CPU_SUPPORT
diff --git a/arch/riscv/cpu/fu540/Kconfig b/arch/riscv/cpu/fu540/Kconfig
index 53e19635c8..ac3f183342 100644
--- a/arch/riscv/cpu/fu540/Kconfig
+++ b/arch/riscv/cpu/fu540/Kconfig
@@ -10,7 +10,7 @@ config SIFIVE_FU540
 	select SPL_RAM if SPL
 	imply CPU
 	imply CPU_RISCV
-	imply RISCV_TIMER
+	imply RISCV_TIMER if (RISCV_SMODE || SPL_RISCV_SMODE)
 	imply SIFIVE_CLINT if (RISCV_MMODE || SPL_RISCV_MMODE)
 	imply CMD_CPU
 	imply SPL_CPU_SUPPORT
diff --git a/arch/riscv/cpu/generic/Kconfig b/arch/riscv/cpu/generic/Kconfig
index b2cb155d6d..f4c2e2643c 100644
--- a/arch/riscv/cpu/generic/Kconfig
+++ b/arch/riscv/cpu/generic/Kconfig
@@ -7,7 +7,7 @@ config GENERIC_RISCV
 	select ARCH_EARLY_INIT_R
 	imply CPU
 	imply CPU_RISCV
-	imply RISCV_TIMER
+	imply RISCV_TIMER if (RISCV_SMODE || SPL_RISCV_SMODE)
 	imply SIFIVE_CLINT if (RISCV_MMODE || SPL_RISCV_MMODE)
 	imply CMD_CPU
 	imply SPL_CPU_SUPPORT
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 6c503ff2b2..10ac5b06d3 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -15,7 +15,6 @@ obj-$(CONFIG_SIFIVE_CLINT) += sifive_clint.o
 obj-$(CONFIG_ANDES_PLIC) += andes_plic.o
 obj-$(CONFIG_ANDES_PLMT) += andes_plmt.o
 else
-obj-$(CONFIG_RISCV_RDTIME) += rdtime.o
 obj-$(CONFIG_SBI) += sbi.o
 obj-$(CONFIG_SBI_IPI) += sbi_ipi.o
 endif
diff --git a/arch/riscv/lib/rdtime.c b/arch/riscv/lib/rdtime.c
deleted file mode 100644
index e128d7fce6..0000000000
--- a/arch/riscv/lib/rdtime.c
+++ /dev/null
@@ -1,38 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0+
-/*
- * Copyright (C) 2018, Anup Patel <anup@brainfault.org>
- * Copyright (C) 2018, Bin Meng <bmeng.cn@gmail.com>
- *
- * The riscv_get_time() API implementation that is using the
- * standard rdtime instruction.
- */
-
-#include <common.h>
-
-/* Implement the API required by RISC-V timer driver */
-int riscv_get_time(u64 *time)
-{
-#ifdef CONFIG_64BIT
-	u64 n;
-
-	__asm__ __volatile__ (
-		"rdtime %0"
-		: "=r" (n));
-
-	*time = n;
-#else
-	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));
-
-	*time = ((u64)hi << 32) | lo;
-#endif
-
-	return 0;
-}