Re: [RFC PATCH v3 2/2] riscv: pgtable: Add "PBMT" extension supported

[Guo Ren]

On Tue, Jun 15, 2021 at 12:11 PM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
>
> On Mon, Jun 14, 2021 at 11:22 PM <guoren@xxxxxxxxxx> wrote:
> >
> > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> >
> > "PBMT" - Page-Based Memory Types (see Link for detail), current it
> > has defined 3 memory types [62:61] in PTE:
> >  - WB 00 "Cacheable 'main memory'"
> >  - NC 01 "Noncacheable 'main memory'"
> >  - IO 11 "Non-cacheable non-idempotent 'I/O'"
> >
> > The patch not only implements the current PBMT extension but also
> > considers future scalability. It uses 3 words of image header to
> > store 8 memory types' values plus a mask value. That means there
> > are still 5 memory types reserved for future scalability.
>
> This is the worst work-around to the Linux RISC-V patch acceptance
> policy.
>
> Passing PTE attributes in the Linux Image header means boot-loaders
> will have to update the image header before jumping to Linux kernel.
> Basically, this is changing the Linux boot-process by adding platform
> specific image header updation step.
>
> Further, this patch is doing too many things in one-go. I needs to be
> broken down into smaller fine-grained patches.
Next time, I'll separate it into below patches:
 - riscv: pgtable: Fixup _PAGE_CHG_MASK usage
 - riscv: pgtable: Add "PBMT" extension supported
 - riscv: pgtable: Add vendor custom "PBMT" definitions interface
How?

>
> I totally disapprove of this patch in it's current shape since the
> Linux boot-protocol should not have any platform specific part.
I think you mean we shouldn't modify the uImage header.

How about parsing dtb before setup_vm (It's a very early stage before
mmu enabled)?  eg:
        cpus {
                ...
                rv64-pbmt-extension;
                rv64-pbmt-custom-remapping = <[mask] [type0] [type1] [type2]>;

>
> Also, please don't CC RVI mailing list for Linux patches because
> the people can post to RVI mailing list only by joining it.
Okay, I'll remove the RVI mailing list. If I needed to, I would send a
notification email to RVI separately.

--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/