linux-kernel - Re: [PATCH v2 1/4] RISC-V: Fix ioremap_cache() and ioremap

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Date:   Thu, 22 Sep 2022 09:35:56 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     apatel@...tanamicro.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>, atishp@...shpatra.org,
        heiko@...ech.de, anup@...infault.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mchitale@...tanamicro.com
Subject:     Re: [PATCH v2 1/4] RISC-V: Fix ioremap_cache() and ioremap_wc() for systems with Svpbmt

On Thu, 15 Sep 2022 19:24:55 PDT (-0700), apatel@...tanamicro.com wrote:
> Hi Palmer,
>
> On Tue, Aug 30, 2022 at 10:17 AM Anup Patel <apatel@...tanamicro.com> wrote:
>>
>> Currently, all flavors of ioremap_xyz() function maps to the generic
>> ioremap() which means any ioremap_xyz() call will always map the
>> target memory as IO using _PAGE_IOREMAP page attributes. This breaks
>> ioremap_cache() and ioremap_wc() on systems with Svpbmt because memory
>> remapped using ioremap_cache() and ioremap_wc() will use _PAGE_IOREMAP
>> page attributes.
>>
>> To address above (just like other architectures), we implement RISC-V
>> specific ioremap_cache() and ioremap_wc() which maps memory using page
>> attributes as defined by the Svpbmt specification.
>>
>> Fixes: ff689fd21cb1 ("riscv: add RISC-V Svpbmt extension support")
>> Co-developed-by: Mayuresh Chitale <mchitale@...tanamicro.com>
>> Signed-off-by: Mayuresh Chitale <mchitale@...tanamicro.com>
>> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
>
> This is a crucial RC fix. Can you please take this ?

Sorry I missed this, I thought it was just part of the rest of this 
patch set.  That said, I'm not actually sure this is a critical fix: 
sure it's a performance problem, and if some driver is expecting 
ioremap_cache() to go fast then possibly a pretty big one, but the only 
Svpmbt hardware that exists is the D1 and that was just supported this 
release so it's not a regression.  Maybe that's a bit pedantic, but all 
this travel has kind of made things a mess and I'm trying to make sure 
nothing goes off the rails.

Probably a pointless distinction as it'll just get backported anyway, 
but I'm going to hold off on this for now -- it generally looks OK, but 
I don't get back until this weekend and I'm super tired so I'm trying to 
avoid screwing anything up.

>
> Regards,
> Anup
>
>> ---
>>  arch/riscv/include/asm/io.h      | 10 ++++++++++
>>  arch/riscv/include/asm/pgtable.h |  2 ++
>>  2 files changed, 12 insertions(+)
>>
>> diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
>> index 69605a474270..07ac63999575 100644
>> --- a/arch/riscv/include/asm/io.h
>> +++ b/arch/riscv/include/asm/io.h
>> @@ -133,6 +133,16 @@ __io_writes_outs(outs, u64, q, __io_pbr(), __io_paw())
>>  #define outsq(addr, buffer, count) __outsq((void __iomem *)addr, buffer, count)
>>  #endif
>>
>> +#ifdef CONFIG_MMU
>> +#define ioremap_wc(addr, size)         \
>> +       ioremap_prot((addr), (size), _PAGE_IOREMAP_WC)
>> +#endif
>> +
>>  #include <asm-generic/io.h>
>>
>> +#ifdef CONFIG_MMU
>> +#define ioremap_cache(addr, size)      \
>> +       ioremap_prot((addr), (size), _PAGE_KERNEL)
>> +#endif
>> +
>>  #endif /* _ASM_RISCV_IO_H */
>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>> index 7ec936910a96..346b7c1a3eeb 100644
>> --- a/arch/riscv/include/asm/pgtable.h
>> +++ b/arch/riscv/include/asm/pgtable.h
>> @@ -182,6 +182,8 @@ extern struct pt_alloc_ops pt_ops __initdata;
>>  #define PAGE_TABLE             __pgprot(_PAGE_TABLE)
>>
>>  #define _PAGE_IOREMAP  ((_PAGE_KERNEL & ~_PAGE_MTMASK) | _PAGE_IO)
>> +#define _PAGE_IOREMAP_WC       ((_PAGE_KERNEL & ~_PAGE_MTMASK) | \
>> +                                _PAGE_NOCACHE)
>>  #define PAGE_KERNEL_IO         __pgprot(_PAGE_IOREMAP)
>>
>>  extern pgd_t swapper_pg_dir[];
>> --
>> 2.34.1
>>