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

["Heiko Stübner" <heiko@sntech.de>]

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)))
> 





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