[U-Boot] [PATCH 04/19] cpu: Add a RISC-V CPU driver

[Bin Meng]

Hi Lukas,

On Thu, Nov 15, 2018 at 5:57 AM Auer, Lukas
<lukas.auer at aisec.fraunhofer.de> wrote:
>
> Hi Bin,
>
> On Tue, 2018-11-13 at 00:21 -0800, Bin Meng wrote:
> > This adds a driver for RISC-V CPU. Note the driver will bind
> > a RISC-V timer driver if "timebase-frequency" property is
> > present in the device tree.
> >
> > Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> > ---
> >
>
> Since we have the CPU driver, we could also enable CMD_CPU.
>

Agreed. Will do in v2.

> >  drivers/cpu/Kconfig     |   6 +++
> >  drivers/cpu/Makefile    |   1 +
> >  drivers/cpu/riscv_cpu.c | 117
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 124 insertions(+)
> >  create mode 100644 drivers/cpu/riscv_cpu.c
> >
> > diff --git a/drivers/cpu/Kconfig b/drivers/cpu/Kconfig
> > index d405200..3d5729f 100644
> > --- a/drivers/cpu/Kconfig
> > +++ b/drivers/cpu/Kconfig
> > @@ -13,3 +13,9 @@ config CPU_MPC83XX
> >       select CLK_MPC83XX
> >       help
> >         Support CPU cores for SoCs of the MPC83xx series.
> > +
> > +config CPU_RISCV
> > +     bool "Enable RISC-V CPU driver"
> > +     depends on CPU && RISCV
> > +     help
> > +       Support CPU cores for RISC-V architecture.
> > diff --git a/drivers/cpu/Makefile b/drivers/cpu/Makefile
> > index 858b037..be0300c 100644
> > --- a/drivers/cpu/Makefile
> > +++ b/drivers/cpu/Makefile
> > @@ -8,4 +8,5 @@ obj-$(CONFIG_CPU) += cpu-uclass.o
> >
> >  obj-$(CONFIG_ARCH_BMIPS) += bmips_cpu.o
> >  obj-$(CONFIG_CPU_MPC83XX) += mpc83xx_cpu.o
> > +obj-$(CONFIG_CPU_RISCV) += riscv_cpu.o
> >  obj-$(CONFIG_SANDBOX) += cpu_sandbox.o
> > diff --git a/drivers/cpu/riscv_cpu.c b/drivers/cpu/riscv_cpu.c
> > new file mode 100644
> > index 0000000..23917db
> > --- /dev/null
> > +++ b/drivers/cpu/riscv_cpu.c
> > @@ -0,0 +1,117 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Copyright (C) 2018, Bin Meng <bmeng.cn at gmail.com>
> > + */
> > +
> > +#include <common.h>
> > +#include <cpu.h>
> > +#include <dm.h>
> > +#include <errno.h>
> > +#include <dm/device-internal.h>
> > +#include <dm/lists.h>
> > +
> > +static int riscv_cpu_get_desc(struct udevice *dev, char *buf, int
> > size)
> > +{
> > +     const char *isa;
> > +
> > +     isa = dev_read_string(dev, "riscv,isa");
> > +     if (size < (strlen(isa) + 1))
> > +             return -ENOSPC;
> > +
> > +     strcpy(buf, isa);
> > +
> > +     return 0;
> > +}
> > +
> > +static int riscv_cpu_get_info(struct udevice *dev, struct cpu_info
> > *info)
> > +{
> > +     const char *mmu;
> > +
> > +     dev_read_u32(dev, "clock-frequency", (u32 *)&info->cpu_freq);
> > +
> > +     mmu = dev_read_string(dev, "mmu-type");
> > +     if (!mmu)
> > +             info->features |= BIT(CPU_FEAT_MMU);
> > +
>
> BBL also disables CPUs without an MMU, so it is good to have this
> information. Where would you disable the CPU in U-Boot? Maybe in
> arch_fixup_fdt() or in the CPU driver?
>

I think disabling CPU only needs to be done if booting to S-mode
payload. If booting to M-mode payload we should leave it as it is.
arch_fixup_fdt() can be a good place to fix up these sort of things
but I think that should be another patch.

> > +     return 0;
> > +}
> > +
> > +static int riscv_cpu_get_count(struct udevice *dev)
> > +{
> > +     ofnode node;
> > +     int num = 0;
> > +
> > +     ofnode_for_each_subnode(node, dev_ofnode(dev->parent)) {
> > +             const char *device_type;
> > +
> > +             device_type = ofnode_read_string(node, "device_type");
> > +             if (!device_type)
> > +                     continue;
> > +             if (strcmp(device_type, "cpu") == 0)
> > +                     num++;
> > +     }
> > +
> > +     return num;
> > +}
> > +
> > +static int riscv_cpu_bind(struct udevice *dev)
> > +{
> > +     struct cpu_platdata *plat = dev_get_parent_platdata(dev);
> > +     struct driver *drv;
> > +     struct udevice *timer;
> > +     int ret;
> > +
> > +     /* save the hart id */
> > +     plat->cpu_id = dev_read_addr(dev);
> > +
> > +     /* first examine the property in current cpu node */
> > +     ret = dev_read_u32(dev, "timebase-frequency", &plat-
> > >timebase_freq);
> > +     /* if not found, then look at the parent /cpus node */
> > +     if (ret)
> > +             dev_read_u32(dev->parent, "timebase-frequency",
> > +                          &plat->timebase_freq);
> > +
> > +     /*
> > +      * Bind riscv-timer driver on hart 0
> > +      *
> > +      * We only instantiate one timer device which is enough for U-
> > Boot.
> > +      * Pass the "timebase-frequency" value as the driver data for
> > the
> > +      * timer device.
> > +      *
> > +      * Return value is not checked since it's possible that the
> > timer
> > +      * driver is not included.
> > +      */
> > +     if (!plat->cpu_id && plat->timebase_freq) {
> > +             drv = lists_driver_lookup_name("riscv_timer");
> > +             if (!drv) {
> > +                     debug("Cannot find the timer driver, not
> > included?\n");
> > +                     return 0;
> > +             }
> > +
> > +             device_bind_with_driver_data(dev, drv, "riscv_timer",
> > +                                          plat->timebase_freq,
> > ofnode_null(),
> > +                                          &timer);
>
> You don't need the timer variable here, you can just pass NULL.
>

Yes, smarter!

> I did not see that you are not checking the return value here, when I
> wrote my previous email regarding the syscon driver. So it is not
> actually a problem if two different device implement the functionality
> for the syscon APIs. I think it is still worth considering to implement
> something like the misc driver I suggested, however.
>

Regards,
Bin