Re: [PATCH 2/2] riscv: implement cache-management errata for T-Head SoCs

Philipp Tomsich
2022-03-31T08:29:56Z

Palmer,

Could you confirm that I correctly understood what you require: is it
that a patch is on the binutils list?

Philipp.

On Thu, 31 Mar 2022 at 10:22, Heiko Stübner <heiko@sntech.de> wrote:
>
> Hi Palmer,
>
> Am Donnerstag, 31. März 2022, 04:30:36 CEST schrieb Palmer Dabbelt:
> > On Mon, 07 Mar 2022 14:46:20 PST (-0800), heiko@sntech.de wrote:
> > > The T-Head C906 and C910 implement a scheme for handling
> > > cache operations different from the generic Zicbom extension.
> > >
> > > Add an errata for it next to the generic dma coherency ops.
> > >
> > > Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> > > ---
> > > arch/riscv/Kconfig.erratas | 10 +++++++
> > > arch/riscv/errata/thead/errata.c | 5 ++++
> > > arch/riscv/include/asm/errata_list.h | 45 ++++++++++++++++++++++++++--
> > > 3 files changed, 57 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/arch/riscv/Kconfig.erratas b/arch/riscv/Kconfig.erratas
> > > index de4002baa1d0..89a6dcb8ac2a 100644
> > > --- a/arch/riscv/Kconfig.erratas
> > > +++ b/arch/riscv/Kconfig.erratas
> > > @@ -50,4 +50,14 @@ config ERRATA_THEAD_PBMT
> > >
> > > If you don't know what to do here, say "Y".
> > >
> > > +config ERRATA_THEAD_CMO
> > > + bool "Apply T-Head cache management errata"
> > > + depends on ERRATA_THEAD && RISCV_DMA_NONCOHERENT
> > > + default y
> > > + help
> > > + This will apply the cache management errata to handle the
> > > + non-standard handling on non-coherent operations on T-Head SoCs.
> > > +
> > > + If you don't know what to do here, say "Y".
> > > +
> > > endmenu
> > > diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> > > index fd8e0538a3f0..11c26c37425f 100644
> > > --- a/arch/riscv/errata/thead/errata.c
> > > +++ b/arch/riscv/errata/thead/errata.c
> > > @@ -33,6 +33,11 @@ static const struct errata_info errata_list[ERRATA_THEAD_NUMBER] = {
> > > .stage = RISCV_ALTERNATIVES_EARLY_BOOT,
> > > .check_func = errata_mt_check_func
> > > },
> > > + {
> > > + .name = "cache-management",
> > > + .stage = RISCV_ALTERNATIVES_BOOT,
> > > + .check_func = errata_mt_check_func
> > > + },
> > > };
> > >
> > > static u32 thead_errata_probe(unsigned int stage, unsigned long archid, unsigned long impid)
> > > diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> > > index 7a2dd61af24d..f7c6805daeab 100644
> > > --- a/arch/riscv/include/asm/errata_list.h
> > > +++ b/arch/riscv/include/asm/errata_list.h
> > > @@ -16,7 +16,8 @@
> > >
> > > #ifdef CONFIG_ERRATA_THEAD
> > > #define ERRATA_THEAD_PBMT 0
> > > -#define ERRATA_THEAD_NUMBER 1
> > > +#define ERRATA_THEAD_CMO 1
> > > +#define ERRATA_THEAD_NUMBER 2
> > > #endif
> > >
> > > #define CPUFEATURE_SVPBMT 0
> > > @@ -104,8 +105,37 @@ asm volatile(ALTERNATIVE( \
> > > #define CBO_CLEAN_A0 ".long 0x25200F"
> > > #define CBO_FLUSH_A0 ".long 0x05200F"
> > >
> > > +/*
> > > + * dcache.ipa rs1 (invalidate, physical address)
> > > + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> > > + * 0000001 01010 rs1 000 00000 0001011
> > > + * dache.iva rs1 (invalida, virtual address)
> > > + * 0000001 00110 rs1 000 00000 0001011
> > > + *
> > > + * dcache.cpa rs1 (clean, physical address)
> > > + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> > > + * 0000001 01001 rs1 000 00000 0001011
> > > + * dcache.cva rs1 (clean, virtual address)
> > > + * 0000001 00100 rs1 000 00000 0001011
> > > + *
> > > + * dcache.cipa rs1 (clean then invalidate, physical address)
> > > + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> > > + * 0000001 01011 rs1 000 00000 0001011
> > > + * dcache.civa rs1 (... virtual address)
> > > + * 0000001 00111 rs1 000 00000 0001011
> > > + *
> > > + * sync.s (make sure all cache operations finished)
> > > + * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> > > + * 0000000 11001 00000 000 00000 0001011
> > > + */
> > > +#define THEAD_INVAL_A0 ".long 0x0265000b"
> > > +#define THEAD_CLEAN_A0 ".long 0x0245000b"
> > > +#define THEAD_FLUSH_A0 ".long 0x0275000b"
> > > +#define THEAD_SYNC_S ".long 0x0190000b"
> >
> > IIRC this came up before, but these really need to get into the
> > assembler as actual instructions.
>
> okay :-) .
>
> But just for my understanding which of the two ways going forward:
> - keep this in the waiting area _until_ a suitable binutils is released
> - use the coded instructions now and convert later once binutils is released
>
> The reason I ask is, that any chip with a t-head core like the Allwinner-D1
> will need this for things like basic networking, so with the binutils
> release schedule, I guess we'd be looking at autumn 2022 at the earliest.
>
>
> Thanks
> Heiko
>
> > > +
> > > #define ALT_CMO_OP(_op, _start, _size) \
> > > -asm volatile(ALTERNATIVE( \
> > > +asm volatile(ALTERNATIVE_2( \
> > > + "nop\n\t" \
> > > "nop\n\t" \
> > > "nop\n\t" \
> > > "nop\n\t" \
> > > @@ -117,7 +147,16 @@ asm volatile(ALTERNATIVE( \
> > > CBO_##_op##_A0 "\n\t" \
> > > "addi a0, a0, %0\n\t" \
> > > "2:\n\t" \
> > > - "bltu a0, %2, 3b\n\t", 0, CPUFEATURE_CMO, CONFIG_RISCV_DMA_NONCOHERENT) \
> > > + "bltu a0, %2, 3b\n\t" \
> > > + "nop", 0, CPUFEATURE_CMO, CONFIG_RISCV_DMA_NONCOHERENT, \
> > > + "mv a0, %1\n\t" \
> > > + "j 2f\n\t" \
> > > + "3:\n\t" \
> > > + THEAD_##_op##_A0 "\n\t" \
> > > + "addi a0, a0, %0\n\t" \
> > > + "2:\n\t" \
> > > + "bltu a0, %2, 3b\n\t" \
> > > + THEAD_SYNC_S, THEAD_VENDOR_ID, ERRATA_THEAD_CMO, CONFIG_ERRATA_THEAD_CMO) \
> > > : : "I"(L1_CACHE_BYTES), "r"((_start) & ~(L1_CACHE_BYTES - 1)), \
> > > "r"(ALIGN((_start) + (_size), L1_CACHE_BYTES)))
> >
>
>
>
>