linux-kernel - Re: [PATCH 1/2] riscv: errata: fix T-Head dcache.cva encoding

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Date:   Tue, 27 Dec 2022 18:04:55 +0800
From:   Icenowy Zheng <uwu@...nowy.me>
To:     Guo Ren <guoren@...nel.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heiko Stuebner <heiko@...ech.de>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: errata: fix T-Head dcache.cva encoding

在 2022-12-27星期二的 10:47 +0800，Guo Ren写道：
> Good catch. But I hope c906/910 can directly use paddr here. It's
> unnecessary to cause software translation & mmu translation here.

This could be an enhancement independent of this patchset.

In addition, I think this is some remaining of the design of the
original patchset, in which adds Zicbom support and then Xtheadcmo
support as some errata.

> 
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-
> noncoherent.c
> index b0add983530a..30650a0c4481 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -24,13 +24,13 @@ void arch_sync_dma_for_device(phys_addr_t paddr,
> size_t size,
> 
>         switch (dir) {
>         case DMA_TO_DEVICE:
> -               ALT_CMO_OP(clean, vaddr, size,
> riscv_cbom_block_size);
> +               ALT_CMO_OP(clean, vaddr, paddr, size,
> riscv_cbom_block_size);

Maybe the macro should be renamed as ALT_CMO_OP_VPA or similar thing,
that means both VA and PA are provided and the most efficient one will
be chosen, because CMO operations with PA is still some T-Head-only
thing (Zicbom only supports VA).

>                 break;
>         case DMA_FROM_DEVICE:
> -               ALT_CMO_OP(clean, vaddr, size,
> riscv_cbom_block_size);
> +               ALT_CMO_OP(clean, vaddr, paddr, size,
> riscv_cbom_block_size);
>                 break;
>         case DMA_BIDIRECTIONAL:
> -               ALT_CMO_OP(flush, vaddr, size,
> riscv_cbom_block_size);
> +               ALT_CMO_OP(flush, vaddr, paddr, size,
> riscv_cbom_block_size);
>                 break;
>         default:
>                 break;
> @@ -47,7 +47,7 @@ void arch_sync_dma_for_cpu(phys_addr_t paddr,
> size_t size,
>                 break;
>         case DMA_FROM_DEVICE:
>         case DMA_BIDIRECTIONAL:
> -               ALT_CMO_OP(flush, vaddr, size,
> riscv_cbom_block_size);
> +               ALT_CMO_OP(flush, vaddr, paddr, size,
> riscv_cbom_block_size);
>                 break;
>         default:
>                 break;
> @@ -57,8 +57,9 @@ void arch_sync_dma_for_cpu(phys_addr_t paddr,
> size_t size,
>  void arch_dma_prep_coherent(struct page *page, size_t size)
>  {
>         void *flush_addr = page_address(page);
> +       phys_addr_t paddr = PFN_PHYS(page_to_pfn(x));
> 
> -       ALT_CMO_OP(flush, flush_addr, size, riscv_cbom_block_size);
> +       ALT_CMO_OP(flush, flush_addr, paddr, size,
> riscv_cbom_block_size);
>  }
> 
> On Tue, Dec 27, 2022 at 10:03 AM Icenowy Zheng <uwu@...nowy.me>
> wrote:
> > 
> > The dcache.cva encoding shown in the comments are wrong, it's for
> > dcache.cval1 (which is restricted to L1) instead.
> > 
> > Fix this in the comment and in the hardcoded instruction.
> > 
> > Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
> > ---
> > The code is tested on a LiteX SoC with OpenC906 core, and it
> > successfully boots to Systemd on a SD card connected to LiteSDCard.
> > 
> > This change should be not noticable on C906, but on multi-core C910
> > cluster it should fixes something. Unfortunately TH1520 seems to be
> > not
> > so ready to test mainline patches on.
> > 
> >  arch/riscv/include/asm/errata_list.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/riscv/include/asm/errata_list.h
> > b/arch/riscv/include/asm/errata_list.h
> > index 4180312d2a70..605800bd390e 100644
> > --- a/arch/riscv/include/asm/errata_list.h
> > +++ b/arch/riscv/include/asm/errata_list.h
> > @@ -102,7 +102,7 @@ asm
> > volatile(ALTERNATIVE(                                           \
> >   * | 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
> > + *   0000001    00101      rs1       000      00000  0001011
> >   *
> >   * dcache.cipa rs1 (clean then invalidate, physical address)
> >   * | 31 - 25 | 24 - 20 | 19 - 15 | 14 - 12 | 11 - 7 | 6 - 0 |
> > @@ -115,7 +115,7 @@ asm
> > volatile(ALTERNATIVE(                                           \
> >   *   0000000    11001     00000      000      00000  0001011
> >   */
> >  #define THEAD_inval_A0 ".long 0x0265000b"
> > -#define THEAD_clean_A0 ".long 0x0245000b"
> > +#define THEAD_clean_A0 ".long 0x0255000b"
> >  #define THEAD_flush_A0 ".long 0x0275000b"
> >  #define THEAD_SYNC_S   ".long 0x0190000b"
> > 
> > --
> > 2.38.1
> > 
> 
>