[U-Boot] [PATCH v3 16/25] riscv: Update supports_extension() to use desc from cpu driver

[Bin Meng]

Hi Lukas,

On Wed, Dec 12, 2018 at 7:40 AM Auer, Lukas
<lukas.auer at aisec.fraunhofer.de> wrote:
>
> Hi Bin,
>
> On Tue, 2018-12-11 at 01:34 -0800, Bin Meng wrote:
> > This updates supports_extension() implementation to use the desc
> > string from the cpu driver whenever possible, which avoids the
> > reading of misa CSR for S-mode U-Boot.
> >
> > Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> >
> > ---
> >
> > Changes in v3:
> > - new patch to update supports_extension() to use desc from cpu
> > driver
> >
> > Changes in v2: None
> >
> >  arch/riscv/cpu/cpu.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> > index d3c59da..704ae70 100644
> > --- a/arch/riscv/cpu/cpu.c
> > +++ b/arch/riscv/cpu/cpu.c
> > @@ -5,8 +5,10 @@
> >
> >  #include <common.h>
> >  #include <cpu.h>
> > +#include <dm.h>
> >  #include <log.h>
> >  #include <asm/csr.h>
> > +#include <dm/uclass-internal.h>
> >
> >  /*
> >   * prior_stage_fdt_address must be stored in the data section since
> > it is used
> > @@ -16,7 +18,21 @@ phys_addr_t prior_stage_fdt_address
> > __attribute__((section(".data")));
> >
> >  static inline bool supports_extension(char ext)
> >  {
> > +#ifdef CONFIG_CPU
> > +     struct udevice *dev;
> > +     char desc[32];
> > +
> > +     uclass_find_first_device(UCLASS_CPU, &dev);
> > +     if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> > +             /* skip the first 4 characters (rv32|rv64) */
> > +             if (strchr(desc + 4, ext))
> > +                     return true;
> > +     }
> > +
> > +     return false;
> > +#else
> >       return csr_read(misa) & (1 << (ext - 'a'));
>
> This should not be used in supervisor mode, so that we don't need a
> patched BBL. I think it is better to use #elif
> defined(CONFIG_RISCV_MMODE) here.
>

OK, will do in v4.

> There should also be a warning message to the user if
> supports_extension() does not have a way to determine the available
> extensions (supervisor-mode and no CONFIG_CPU or CONFIG_CPU, but no
> device found). This would help to prevent difficult-to-debug errors
> caused by part of the initialization missing.
>

Will add a warning message for S-mode without CPU. I don't think we
should warn CONFIG_CPU but no device found case as it has already been
covered in riscv_cpu_probe().

Regards,
Bin