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

[Bin Meng]

Hi Tom,

On Tue, Nov 14, 2023 at 6:59 AM Tom Rini <trini at konsulko.com> wrote:
>
> On Mon, Nov 13, 2023 at 03:28:13PM -0700, Simon Glass wrote:
> > Hi Bin,
> >
> > On Mon, 13 Nov 2023 at 15:08, Bin Meng <bmeng.cn at gmail.com> wrote:
> > >
> > > Hi Simon,
> > >
> > > On Mon, Nov 13, 2023 at 4:03 AM Simon Glass <sjg at 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 at chromium.org>
> > > > Suggested-by: Bin Meng <bmeng.cn at 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?)
>
> Maybe the issue even is that on x86 we're being too imprecise in our
> build rules (and also on RISC-V, another issue). Today on x86 this fails
> because we say -mno-mmx -mno-sse and not also -msoft-float. I can just
> turn that on, on all x86 targets today and things build. Would that not
> also fix the truetype issue?

One can easily turn on compiler flags for x86 (and for RISC-V too) to
tell the compiler to generate floating point instructions if it sees
fit.

However on x86 and RISC-V there are configurations needed to program
the CPU registers to turn on the hardware FP, otherwise an exception
will be generated.

Regards,
Bin