Messages in this thread | | | From | Guo Ren <> | Date | Thu, 16 Sep 2021 08:48:57 +0800 | Subject | Re: [RFC PATCH V4 2/6] riscv: errata: pgtable: Add custom Svpbmt supported for Allwinner D1 |
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On Wed, Sep 15, 2021 at 3:47 PM Christoph Hellwig <hch@lst.de> wrote: > > This is the wrong way around. We need to design around the PBMT > definitions. I've defined them in arch/riscv/include/asm/pgtable-bits.h first, that follow current latest draft. Then I undefine them in errata/thead/errata.c to illustrate we should follow standard PBMT, not a custom one.
> If we want to hack in support for completely broken SOCs > that intentionally violate the specification it should be done after > the fact, When c9xx was released in 2018, there is no clear direction for how to solve the non-coherent problem. We just thought PBMT is the correct direction, but we can't predict how encoding exactly in the highest bits. (Maybe we should keep the highest bits zero for _P/SXXX in pgtable.h, but it was really hard to guess at that time.) So don't imply we "intentionally" here! When the svpbmt is frozen in the future, we would follow that in our next-generation processor.
> in a separate patch, using alternatives and clearly documenting > how broken these SOCs are. Okay, I would separate errata into another patch.
About documenting, I've illustrated c9xx PTE format's detail and using undef _PAGE_XXX to show that we replaced standard's in errata:
+/* + * T-HEAD C9xx PTE format: + * | 63 | 62 | 61 | 60 | 59-8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 + * SO C B SH RSW D A G U X W R V + * ^ ^ ^ ^ ^ + * BIT(63): SO - Strong Order + * BIT(62): C - Cacheable + * BIT(61): B - Bufferable + * BIT(60): SH - Shareable + * + * MT_MASK : [63 - 59] + * MT_PMA : C + SH + * MT_NC : (none) + * MT_IO : SO + */ +#undef _PAGE_MT_MASK +#undef _PAGE_MT_PMA +#undef _PAGE_MT_NC +#undef _PAGE_MT_IO + +#define _PAGE_MT_MASK 0xf800000000000000 +#define _PAGE_MT_PMA 0x5000000000000000 +#define _PAGE_MT_NC 0x0 +#define _PAGE_MT_IO 0x8000000000000000 +#endif
-- Best Regards Guo Ren
ML: https://lore.kernel.org/linux-csky/
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