[U-Boot] [PATCH v7 4/4] RISC-V: Add S-mode timer implementation
Bin Meng
bmeng.cn at gmail.com
Mon Dec 3 07:26:00 UTC 2018
Hi Anup,
On Mon, Dec 3, 2018 at 3:19 PM Anup Patel <anup at brainfault.org> wrote:
>
> On Mon, Dec 3, 2018 at 12:32 PM Bin Meng <bmeng.cn at gmail.com> wrote:
> >
> > Hi Anup,
> >
> > On Mon, Dec 3, 2018 at 2:43 PM Anup Patel <anup at brainfault.org> wrote:
> > >
> > > On Mon, Dec 3, 2018 at 12:06 PM Bin Meng <bmeng.cn at gmail.com> wrote:
> > > >
> > > > Hi Anup,
> > > >
> > > > On Mon, Dec 3, 2018 at 1:28 PM Anup Patel <anup at brainfault.org> wrote:
> > > > >
> > > > > When running in S-mode, we can use rdtime and rdtimeh instructions
> > > > > for reading timer ticks (just like Linux). The frequency of timer
> > > > > ticks is passed by prior booting stages in "timebase-frequency" DT
> > > > > property of the "/cpus" DT node.
> > > > >
> > > > > This patch provides a generic timer implementation for U-Boot
> > > > > running in S-mode. For U-Boot running in M-mode, specific timer
> > > > > drivers will have to be provided.
> > > > >
> > > > > Signed-off-by: Anup Patel <anup at brainfault.org>
> > > > > ---
> > > > > arch/Kconfig | 1 -
> > > > > arch/riscv/Kconfig | 22 +++++++++++----
> > > > > arch/riscv/lib/Makefile | 1 +
> > > > > arch/riscv/lib/time.c | 60 +++++++++++++++++++++++++++++++++++++++++
> > > > > 4 files changed, 78 insertions(+), 6 deletions(-)
> > > > > create mode 100644 arch/riscv/lib/time.c
> > > > >
> > > > > diff --git a/arch/Kconfig b/arch/Kconfig
> > > > > index 9fdd2f7e66..a4fcb3522d 100644
> > > > > --- a/arch/Kconfig
> > > > > +++ b/arch/Kconfig
> > > > > @@ -72,7 +72,6 @@ config RISCV
> > > > > imply BLK
> > > > > imply CLK
> > > > > imply MTD
> > > > > - imply TIMER
> > > >
> > > > No, please don't do this.
> > >
> > > I am removing here but selecting it only for M-mode U-Boot.
> > >
> > > >
> > > > > imply CMD_DM
> > > > >
> > > > > config SANDBOX
> > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > > index 732a357a99..20a060454b 100644
> > > > > --- a/arch/riscv/Kconfig
> > > > > +++ b/arch/riscv/Kconfig
> > > > > @@ -44,6 +44,23 @@ config ARCH_RV64I
> > > > >
> > > > > endchoice
> > > > >
> > > > > +choice
> > > > > + prompt "Run Mode"
> > > > > + default RISCV_MMODE
> > > > > +
> > > > > +config RISCV_MMODE
> > > > > + bool "Machine"
> > > > > + select TIMER
> > > > > + help
> > > > > + Choose this option to build U-Boot for RISC-V M-Mode.
> > > > > +
> > > > > +config RISCV_SMODE
> > > > > + bool "Supervisor"
> > > > > + help
> > > > > + Choose this option to build U-Boot for RISC-V S-Mode.
> > > > > +
> > > > > +endchoice
> > > > > +
> > > >
> > > > The above changes deserve separate patch, or merge that in the 1st
> > > > patch in the series.
> > >
> > > Sure, I will put Kconfig changes as separate patch.
> > >
> > > >
> > > > > config RISCV_ISA_C
> > > > > bool "Emit compressed instructions"
> > > > > default y
> > > > > @@ -55,11 +72,6 @@ config RISCV_ISA_C
> > > > > config RISCV_ISA_A
> > > > > def_bool y
> > > > >
> > > > > -config RISCV_SMODE
> > > > > - bool "Run in S-Mode"
> > > > > - help
> > > > > - Enable this option to build U-Boot for RISC-V S-Mode
> > > > > -
> > > > > config 32BIT
> > > > > bool
> > > > >
> > > > > diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> > > > > index b58db89752..98aa6d40e7 100644
> > > > > --- a/arch/riscv/lib/Makefile
> > > > > +++ b/arch/riscv/lib/Makefile
> > > > > @@ -12,6 +12,7 @@ obj-y += cache.o
> > > > > obj-y += interrupts.o
> > > > > obj-y += reset.o
> > > > > obj-y += setjmp.o
> > > > > +obj-$(CONFIG_RISCV_SMODE) += time.o
> > > > >
> > > > > # For building EFI apps
> > > > > CFLAGS_$(EFI_CRT0) := $(CFLAGS_EFI)
> > > > > diff --git a/arch/riscv/lib/time.c b/arch/riscv/lib/time.c
> > > > > new file mode 100644
> > > > > index 0000000000..077e568ca6
> > > > > --- /dev/null
> > > > > +++ b/arch/riscv/lib/time.c
> > > > > @@ -0,0 +1,60 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0+
> > > > > +/*
> > > > > + * Copyright (C) 2018, Anup Patel <anup at brainfault.org>
> > > > > + */
> > > > > +
> > > > > +#include <common.h>
> > > > > +#include <fdtdec.h>
> > > > > +
> > > > > +DECLARE_GLOBAL_DATA_PTR;
> > > > > +
> > > > > +static unsigned int tbclk;
> > > > > +
> > > > > +static void setup_tbclk(void)
> > > > > +{
> > > > > + int cpus;
> > > > > +
> > > > > + if (!gd->fdt_blob || tbclk)
> > > > > + return;
> > > > > +
> > > > > + cpus = fdt_path_offset(gd->fdt_blob, "/cpus");
> > > > > + if (cpus < 0) {
> > > > > + debug("%s: Missing /cpus node\n", __func__);
> > > > > + return;
> > > > > + }
> > > > > +
> > > > > + tbclk = fdtdec_get_int(gd->fdt_blob, cpus,
> > > > > + "timebase-frequency", 1000000);
> > > > > +}
> > > > > +
> > > > > +ulong notrace get_tbclk(void)
> > > > > +{
> > > > > + setup_tbclk();
> > > > > +
> > > > > + return tbclk;
> > > > > +}
> > > > > +
> > > > > +#ifdef CONFIG_64BIT
> > > > > +uint64_t notrace get_ticks(void)
> > > > > +{
> > > > > + unsigned long n;
> > > > > +
> > > > > + __asm__ __volatile__ (
> > > > > + "rdtime %0"
> > > > > + : "=r" (n));
> > > > > + return n;
> > > > > +}
> > > > > +#else
> > > > > +uint64_t notrace get_ticks(void)
> > > > > +{
> > > > > + uint32_t 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));
> > > > > + return ((uint64_t)hi << 32) | lo;
> > > > > +}
> > > > > +#endif
> > > > > --
> > > >
> > > > The proper way to implement timer driver is via DM. Could you please
> > > > implement a DM timer driver for S-mode?
> > > >
> > > > The M-mode timer driver is @ http://patchwork.ozlabs.org/patch/996892/, FYI.
> > >
> > > "rdtime" is an instruction. It's not an device for which we can
> > > implement DM driver.
> > >
> >
> > Yes, I know. But that does not mean we cannot write a driver to do the
> > paper work.
>
> There is no DT node for "rdtime" so how should we probe the DM driver.
>
I think you can do some modification to create the S-mode timer driver
based on the M-mode driver patch I provided.
In the riscv_timer_probe(), do not require syscon driver to be loaded,
ie: not calling syscon_get_by_driver_data(). In the
riscv_timer_get_count(), implement that with rdtime for S-mode.
> >
> > > This is similar to how U-Boot ARM64 uses CNTPCT_EL0 register.
> > >
> > > We cannot use DM driver here.
> > >
> >
> > The issue is that eventually we will migrate all U-Boot device drivers
> > to DM, which means get_tbclk() and get_ticks() you implemented will be
> > broken someday in the future.
>
> Yes, I agree we should have DM driver whenever possible but sometime
> there is no DT bindings for things like timer because it's part of CPU
> instruction or CSRs
>
Regards,
Bin
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