Re: [PATCH v4 09/12] x86: Enable SSE in 64-bit mode

[Simon Glass <sjg@chromium.org>]

Hi Bin,

On Mon, 13 Nov 2023 at 15:08, Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Hi Simon,
>
> On Mon, Nov 13, 2023 at 4:03 AM Simon Glass <sjg@chromium.org> wrote:
> >
> > This is needed to support Truetype fonts. In any case, the compiler
> > expects SSE to be available in 64-bit mode. Provide an option to enable
> > SSE so that hardware floating-point arithmetic works.
> >
> > Signed-off-by: Simon Glass <sjg@chromium.org>
> > Suggested-by: Bin Meng <bmeng.cn@gmail.com>
> > ---
> >
> > Changes in v4:
> > - Use a Kconfig option
> >
> >  arch/x86/Kconfig          |  8 ++++++++
> >  arch/x86/config.mk        |  4 ++++
> >  arch/x86/cpu/x86_64/cpu.c | 12 ++++++++++++
> >  drivers/video/Kconfig     |  1 +
> >  4 files changed, 25 insertions(+)
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 99e59d94c606..6b532d712ee8 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -723,6 +723,14 @@ config ROM_TABLE_SIZE
> >         hex
> >         default 0x10000
> >
> > +config X86_HARDFP
> > +       bool "Support hardware floating point"
> > +       help
> > +         U-Boot generally does not make use of floating point. Where this is
> > +         needed, it can be enabled using this option. This adjusts the
> > +         start-up code for 64-bit mode and changes the compiler options for
> > +         64-bit to enable SSE.
>
> As discussed in another thread, this option should be made global to
> all architectures and by default no.
>
> > +
> >  config HAVE_ITSS
> >         bool "Enable ITSS"
> >         help
> > diff --git a/arch/x86/config.mk b/arch/x86/config.mk
> > index 26ec1af2f0b0..2e3a7119e798 100644
> > --- a/arch/x86/config.mk
> > +++ b/arch/x86/config.mk
> > @@ -27,9 +27,13 @@ ifeq ($(IS_32BIT),y)
> >  PLATFORM_CPPFLAGS += -march=i386 -m32
> >  else
> >  PLATFORM_CPPFLAGS += $(if $(CONFIG_SPL_BUILD),,-fpic) -fno-common -march=core2 -m64
> > +
> > +ifndef CONFIG_X86_HARDFP
> >  PLATFORM_CPPFLAGS += -mno-mmx -mno-sse
> >  endif
> >
> > +endif # IS_32BIT
> > +
> >  PLATFORM_RELFLAGS += -fdata-sections -ffunction-sections -fvisibility=hidden
> >
> >  KBUILD_LDFLAGS += -Bsymbolic -Bsymbolic-functions
> > diff --git a/arch/x86/cpu/x86_64/cpu.c b/arch/x86/cpu/x86_64/cpu.c
> > index 2647bff891f8..5ea746ecce4d 100644
> > --- a/arch/x86/cpu/x86_64/cpu.c
> > +++ b/arch/x86/cpu/x86_64/cpu.c
> > @@ -10,6 +10,7 @@
> >  #include <init.h>
> >  #include <asm/cpu.h>
> >  #include <asm/global_data.h>
> > +#include <asm/processor-flags.h>
> >
> >  DECLARE_GLOBAL_DATA_PTR;
> >
> > @@ -39,11 +40,22 @@ int x86_mp_init(void)
> >         return 0;
> >  }
> >
> > +/* enable SSE features for hardware floating point */
> > +static void setup_sse_features(void)
> > +{
> > +       asm ("mov %%cr4, %%rax\n" \
> > +       "or  %0, %%rax\n" \
> > +       "mov %%rax, %%cr4\n" \
> > +       : : "i" (X86_CR4_OSFXSR | X86_CR4_OSXMMEXCPT) : "eax");
> > +}
> > +
> >  int x86_cpu_reinit_f(void)
> >  {
> >         /* set the vendor to Intel so that native_calibrate_tsc() works */
> >         gd->arch.x86_vendor = X86_VENDOR_INTEL;
> >         gd->arch.has_mtrr = true;
> > +       if (IS_ENABLED(CONFIG_X86_HARDFP))
> > +               setup_sse_features();
> >
> >         return 0;
> >  }
> > diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
> > index 6f319ba0d544..39c82521be16 100644
> > --- a/drivers/video/Kconfig
> > +++ b/drivers/video/Kconfig
> > @@ -180,6 +180,7 @@ config CONSOLE_ROTATION
> >
> >  config CONSOLE_TRUETYPE
> >         bool "Support a console that uses TrueType fonts"
> > +       select X86_HARDFP if X86
>
> This should be "depends on HARDFP", indicating that the TrueType
> library is using hardware fp itself, and user has to explicitly turn
> the hardware fp Kconfig option on.

So you mean 'depends on HARDFP if X86'  ? After all, this is only for
X86 - other archs can use softfp which is already enabled, as I
understand it.

>
> "Select" does not work for architectures that does not have the
> "enabling hardware fp" logic in place.
>
> >         help
> >           TrueTrype fonts can provide outline-drawing capability rather than
> >           needing to provide a bitmap for each font and size that is needed.
> > --

I still don't think we are on the same page here. I would prefer to
just enable the options without any option. I really don't want to get
into RISC-V stuff - that is a separate concern.

From my POV it seems that x86 is special in that:
- it uses hardfp
- hardfp is always available in any CPU with 64-bit support (I think?)

So please can you be a bit more specific here?

Regards,
Simon