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

[Christophe Leroy <christophe.leroy@csgroup.eu>]

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.

> 
> 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@ew.tq-group.com>
> ---
>   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.

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 ?

>   #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

> +
> +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",
> --
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