Re: [PATCH v4 2/4] RISC-V: Fix ioremap_cache() and ioremap_wc() for systems with Svpbmt

[Arnd Bergmann]

On Wed, Oct 19, 2022, at 18:10, Anup Patel wrote:
> On Wed, Oct 19, 2022 at 7:49 PM Heiko Stuebner <heiko@xxxxxxxxx> wrote:
>>
>> Am Mittwoch, 19. Oktober 2022, 15:11:26 CEST schrieb Anup Patel:
>> > 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@xxxxxxxxxxxxxxxx>
>> > Signed-off-by: Mayuresh Chitale <mchitale@xxxxxxxxxxxxxxxx>
>> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
>>
>> Wasn't there discussion around those functions in general in v2?
>
> Yes, there was discussion about a few drivers using ioremap_xyz()
> which is discouraged and drivers should use memremap().
>
> We still need the arch specific ioremap_xyz() functions/macros
> added by this patch because these are required by the generic
> kernel memremap() implementation (refer, kernel/iomem.c).

There is a difference between the strongly discouraged
ioremap_cache() that pretty much has no valid users, and
the ioremap_wt/ioremap_wc functions that are sometimes used
for mapping video framebuffer or similar.

It should be sufficient to provide a arch_memremap_wb()
and no ioremap_cache() to make memremap() work correctly.

      Arnd