[U-Boot] [PATCH v7 4/4] RISC-V: Add S-mode timer implementation

[Bin Meng]

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.

> 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.

Regards,
Bin