Re: [PATCH] powerpc/6xx: set High BAT Enable flag on G2 cores

[Matthias Schiffer]

On Fri, 2023-12-22 at 18:41 +0000, Christophe Leroy wrote:
> Le 22/12/2023 à 09:48, Matthias Schiffer a écrit :
> > [Vous ne recevez pas souvent de courriers de matthias.schiffer@xxxxxxxxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > On Thu, 2023-12-21 at 13:57 +0000, Christophe Leroy wrote:
> > > 
> > > 
> > > Le 21/12/2023 à 13:45, Matthias Schiffer a écrit :
> > > > MMU_FTR_USE_HIGH_BATS is set for G2-based cores (G2_LE, e300cX), but the
> > > > high BATs need to be enabled in HID2 to work. Add register definitions
> > > > and introduce a G2 variant of __setup_cpu_603.
> > > 
> > > Well spotted.
> > > 
> > > I have a mpc8321, hence e300c2. I never had the problem you had.
> > > 
> > > But ... looks like U-boot configuration has CONFIG_HID2_HBE so that's
> > > set by U-boot indeed, that's the reason why I never had that problem.
> > 
> > I'll extend the commit message to mention that U-Boot setting in v2.
> > 
> > 
> > > 
> > > > 
> > > > This fixes boot on CPUs like the MPC5200B with STRICT_KERNEL_RWX enabled.
> > > > 
> > > > Fixes: e4d6654ebe6e ("powerpc/mm/32s: rework mmu_mapin_ram()")
> > > > Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
> > > > ---
> > > >    arch/powerpc/include/asm/cpu_setup.h      |  1 +
> > > >    arch/powerpc/include/asm/reg.h            |  2 ++
> > > >    arch/powerpc/kernel/cpu_setup_6xx.S       | 25 ++++++++++++++++++++++-
> > > >    arch/powerpc/kernel/cpu_specs_book3s_32.h | 10 ++++-----
> > > >    4 files changed, 32 insertions(+), 6 deletions(-)
> > > > 
> > > > 
> > > > I have only tested this on the MPC5200B (G2_LE), but according to the
> > > > e300 manual, e300cX cores should behave the same.
> > > > 
> > > > The Fixes tag is the best I could come up with - I believe that the
> > > > underlying issue of setting USE_HIGH_BATS without actually enabling them
> > > > is as old as Linux's PowerPC implementation, but the specific code
> > > > causing the boot failure was added in the mentioned commit.
> > > 
> > > Agreed, before that only BATs 0 to 3 were used anyway.
> > > There was also BAT 4 used by platforms/embedded6xx/wii.c  , but that's
> > > probably not a G2 ?
> > > 
> > > > 
> > > > Another issue I found in the code is that
> > > > arch/powerpc/platforms/52xx/lite5200_sleep.S uses the SPRN_HID2 definition
> > > > which does not refer to HID2 on the 5200... but that will be for someone
> > > > else to fix, if there is still anyone left using that platform.
> > > 
> > > Maybe file an issue for it at https://github.com/linuxppc/issues/issues
> > > if you don't plan to fix it ?
> > > 
> > > By the way, it looks like the SPRN_HID2 definition we have is very
> > > specific to the IBM 750.
> > > 
> > 
> > IBM 750GX even - googling for IBM 750 came up with several other cores that either don't have HID2,
> > or have it at a different SPR.
> > 
> > 
> > > MPC 750 has SPRN_HID2 as 1011 == 0x3f3 like others.
> > 
> > > > 
> > > > 
> > > > diff --git a/arch/powerpc/include/asm/cpu_setup.h b/arch/powerpc/include/asm/cpu_setup.h
> > > > index 30e2fe3895024..68d804e74d221 100644
> > > > --- a/arch/powerpc/include/asm/cpu_setup.h
> > > > +++ b/arch/powerpc/include/asm/cpu_setup.h
> > > > @@ -35,6 +35,7 @@ void __setup_cpu_750fx(unsigned long offset, struct cpu_spec *spec);
> > > >    void __setup_cpu_7400(unsigned long offset, struct cpu_spec *spec);
> > > >    void __setup_cpu_7410(unsigned long offset, struct cpu_spec *spec);
> > > >    void __setup_cpu_745x(unsigned long offset, struct cpu_spec *spec);
> > > > +void __setup_cpu_g2(unsigned long offset, struct cpu_spec *spec);
> > > > 
> > > >    void __setup_cpu_ppc970(unsigned long offset, struct cpu_spec *spec);
> > > >    void __setup_cpu_ppc970MP(unsigned long offset, struct cpu_spec *spec);
> > > > diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> > > > index 4ae4ab9090a2d..f5641fcd1da85 100644
> > > > --- a/arch/powerpc/include/asm/reg.h
> > > > +++ b/arch/powerpc/include/asm/reg.h
> > > > @@ -617,6 +617,8 @@
> > > >    #endif
> > > >    #define SPRN_HID2      0x3F8           /* Hardware Implementation Register 2 */
> > > 
> > > Should that HID2 be renamed to SPRN_HID2_750 to avoid confusion ?
> > 
> > Makes sense (should the suffix be "750GX"?). I can also add a FIXME comment to lite5200_sleep.S as
> > part of the rename.
> > 
> > 
> > > 
> > > >    #define SPRN_HID2_GEKKO        0x398           /* Gekko HID2 Register */
> > > > +#define SPRN_HID2_G2   0x3F3           /* G2 HID2 Register */
> > > > +#define  HID2_HBE_G2   (1<<18)         /* High BAT Enable (G2) */
> > > >    #define SPRN_IABR      0x3F2   /* Instruction Address Breakpoint Register */
> > > >    #define SPRN_IABR2     0x3FA           /* 83xx */
> > > >    #define SPRN_IBCR      0x135           /* 83xx Insn Breakpoint Control Reg */
> > > > diff --git a/arch/powerpc/kernel/cpu_setup_6xx.S b/arch/powerpc/kernel/cpu_setup_6xx.S
> > > > index f29ce3dd6140f..c67d32e04df9c 100644
> > > > --- a/arch/powerpc/kernel/cpu_setup_6xx.S
> > > > +++ b/arch/powerpc/kernel/cpu_setup_6xx.S
> > > > @@ -81,6 +81,20 @@ _GLOBAL(__setup_cpu_745x)
> > > >           bl      setup_745x_specifics
> > > >           mtlr    r5
> > > >           blr
> > > > +_GLOBAL(__setup_cpu_g2)
> > > > +       mflr    r5
> > > > +BEGIN_MMU_FTR_SECTION
> > > > +       li      r10,0
> > > > +       mtspr   SPRN_SPRG_603_LRU,r10           /* init SW LRU tracking */
> > > > +END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
> > > 
> > > MMU_FTR_NEED_DTLB_SW_LRU is dedicated to e300 core. You should also
> > > remove it from __setup_cpu_603
> > 
> > Will do, thanks.
> 
> Thinking about it once more, can we do even more simple ?
> 
> Why do we need that __setup_cpu_g2() at all ?
> 
> You could just add the following into __set_cpu_603()
> 
> diff --git a/arch/powerpc/kernel/cpu_setup_6xx.S 
> b/arch/powerpc/kernel/cpu_setup_6xx.S
> index c67d32e04df9..7b41e3884866 100644
> --- a/arch/powerpc/kernel/cpu_setup_6xx.S
> +++ b/arch/powerpc/kernel/cpu_setup_6xx.S
> @@ -21,6 +21,11 @@ BEGIN_MMU_FTR_SECTION
>   	li	r10,0
>   	mtspr	SPRN_SPRG_603_LRU,r10		/* init SW LRU tracking */
>   END_MMU_FTR_SECTION_IFSET(MMU_FTR_NEED_DTLB_SW_LRU)
> +BEGIN_MMU_FTR_SECTION
> +	mfspr	r11,SPRN_HID2_G2
> +	oris	r11,r11,HID2_HBE_G2@h
> +	mtspr	SPRN_HID2_G2,r11
> +END_MMU_FTR_SECTION_IFSET(MMU_FTR_USE_HIGH_BATS)
> 
>   BEGIN_FTR_SECTION
>   	bl	__init_fpu_registers
> ---
> 
> By the way, as your register is named SPRN_HID2_G2, the bit would better 
> be named HID2_G2_HBE instead of HID2_HBE_G2 I think.

My intention was to keep this consistent with the SPRN_HID2_GEKKO define.

Regards,
Matthias




> 
> Christophe
> 
> > 
> > > 
> > > > +
> > > > +BEGIN_FTR_SECTION
> > > > +       bl      __init_fpu_registers
> > > > +END_FTR_SECTION_IFCLR(CPU_FTR_FPU_UNAVAILABLE)
> > > > +       bl      setup_common_caches
> > > > +       bl      setup_g2_hid2
> > > > +       mtlr    r5
> > > > +       blr
> > > > 
> > > >    /* Enable caches for 603's, 604, 750 & 7400 */
> > > >    SYM_FUNC_START_LOCAL(setup_common_caches)
> > > > @@ -115,6 +129,16 @@ SYM_FUNC_START_LOCAL(setup_604_hid0)
> > > >           blr
> > > >    SYM_FUNC_END(setup_604_hid0)
> > > > 
> > > > +/* Enable high BATs for G2 (G2_LE, e300cX) */
> > > > +SYM_FUNC_START_LOCAL(setup_g2_hid2)
> > > > +       mfspr   r11,SPRN_HID2_G2
> > > > +       oris    r11,r11,HID2_HBE_G2@h
> > > > +       mtspr   SPRN_HID2_G2,r11
> > > > +       sync
> > > > +       isync
> > > > +       blr
> > > > +SYM_FUNC_END(setup_g2_hid2)
> > > > +
> > > >    /* 7400 <= rev 2.7 and 7410 rev = 1.0 suffer from some
> > > >     * erratas we work around here.
> > > >     * Moto MPC710CE.pdf describes them, those are errata
> > > > @@ -495,4 +519,3 @@ _GLOBAL(__restore_cpu_setup)
> > > >           mtcr    r7
> > > >           blr
> > > >    _ASM_NOKPROBE_SYMBOL(__restore_cpu_setup)
> > > > -
> > > > diff --git a/arch/powerpc/kernel/cpu_specs_book3s_32.h b/arch/powerpc/kernel/cpu_specs_book3s_32.h
> > > > index 3714634d194a1..83f054fcf837c 100644
> > > > --- a/arch/powerpc/kernel/cpu_specs_book3s_32.h
> > > > +++ b/arch/powerpc/kernel/cpu_specs_book3s_32.h
> > > > @@ -69,7 +69,7 @@ static struct cpu_spec cpu_specs[] __initdata = {
> > > >                   .mmu_features           = MMU_FTR_USE_HIGH_BATS,
> > > >                   .icache_bsize           = 32,
> > > >                   .dcache_bsize           = 32,
> > > > -               .cpu_setup              = __setup_cpu_603,
> > > > +               .cpu_setup              = __setup_cpu_g2,
> > > >                   .machine_check          = machine_check_generic,
> > > >                   .platform               = "ppc603",
> > > >           },
> > > > @@ -83,7 +83,7 @@ static struct cpu_spec cpu_specs[] __initdata = {
> > > >                   .mmu_features           = MMU_FTR_USE_HIGH_BATS,
> > > >                   .icache_bsize           = 32,
> > > >                   .dcache_bsize           = 32,
> > > > -               .cpu_setup              = __setup_cpu_603,
> > > > +               .cpu_setup              = __setup_cpu_g2,
> > > >                   .machine_check          = machine_check_83xx,
> > > >                   .platform               = "ppc603",
> > > >           },
> > > > @@ -96,7 +96,7 @@ static struct cpu_spec cpu_specs[] __initdata = {
> > > >                   .mmu_features           = MMU_FTR_USE_HIGH_BATS | MMU_FTR_NEED_DTLB_SW_LRU,
> > > >                   .icache_bsize           = 32,
> > > >                   .dcache_bsize           = 32,
> > > > -               .cpu_setup              = __setup_cpu_603,
> > > > +               .cpu_setup              = __setup_cpu_g2,
> > > >                   .machine_check          = machine_check_83xx,
> > > >                   .platform               = "ppc603",
> > > >           },
> > > > @@ -109,7 +109,7 @@ static struct cpu_spec cpu_specs[] __initdata = {
> > > >                   .mmu_features           = MMU_FTR_USE_HIGH_BATS | MMU_FTR_NEED_DTLB_SW_LRU,
> > > >                   .icache_bsize           = 32,
> > > >                   .dcache_bsize           = 32,
> > > > -               .cpu_setup              = __setup_cpu_603,
> > > > +               .cpu_setup              = __setup_cpu_g2,
> > > >                   .machine_check          = machine_check_83xx,
> > > >                   .num_pmcs               = 4,
> > > >                   .platform               = "ppc603",
> > > > @@ -123,7 +123,7 @@ static struct cpu_spec cpu_specs[] __initdata = {
> > > >                   .mmu_features           = MMU_FTR_USE_HIGH_BATS | MMU_FTR_NEED_DTLB_SW_LRU,
> > > >                   .icache_bsize           = 32,
> > > >                   .dcache_bsize           = 32,
> > > > -               .cpu_setup              = __setup_cpu_603,
> > > > +               .cpu_setup              = __setup_cpu_g2,
> > > >                   .machine_check          = machine_check_83xx,
> > > >                   .num_pmcs               = 4,
> > > >                   .platform               = "ppc603",
> > > > --
> > > > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
> > > > Amtsgericht München, HRB 105018
> > > > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
> > > > https://www.tq-group.com/
> > 
> > --
> > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
> > Amtsgericht München, HRB 105018
> > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
> > https://www.tq-group.com/

-- 
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
https://www.tq-group.com/