[RFC PATCH v2 2/2] soc: renesas: Add L2 cache management for RZ/Five SoC

[Guo Ren]

On Wed, Oct 5, 2022 at 8:54 PM Lad, Prabhakar
<prabhakar.csengg at gmail.com> wrote:
>
> Hi Guo,
>
> On Wed, Oct 5, 2022 at 2:29 AM Guo Ren <guoren at kernel.org> wrote:
> >
> > On Tue, Oct 4, 2022 at 6:32 AM Prabhakar <prabhakar.csengg at gmail.com> wrote:
> > >
> > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>
> > >
> > > On the AX45MP core, cache coherency is a specification option so it may
> > > not be supported. In this case DMA will fail. As a workaround, firstly we
> > > allocate a global dma coherent pool from which DMA allocations are taken
> > > and marked as non-cacheable + bufferable using the PMA region as specified
> > > in the device tree. Synchronization callbacks are implemented to
> > > synchronize when doing DMA transactions.
> > >
> > > The Andes AX45MP core has a Programmable Physical Memory Attributes (PMA)
> > > block that allows dynamic adjustment of memory attributes in the runtime.
> > > It contains a configurable amount of PMA entries implemented as CSR
> > > registers to control the attributes of memory locations in interest.
> > >
> > > Below are the memory attributes supported:
> > > * Device, Non-bufferable
> > > * Device, bufferable
> > > * Memory, Non-cacheable, Non-bufferable
> > > * Memory, Non-cacheable, Bufferable
> > > * Memory, Write-back, No-allocate
> > > * Memory, Write-back, Read-allocate
> > > * Memory, Write-back, Write-allocate
> > > * Memory, Write-back, Read and Write-allocate
> > Seems Svpbmt's PMA, IO, and NC wouldn't fit your requirements, could
> > give a map list of the types of Svpbmt? And give out what you needed,
> > but Svpbmt can't.
> >
> Sorry I didn't get what you meant here, could you please elaborate.
I know there is no pbmt in AX45MP, I am just curious how many physical
memory attributes you would use in linux? It seems only one type used
in the series:
cpu_nocache_area_set -> sbi_ecall(SBI_EXT_ANDES,
SBI_EXT_ANDES_SET_PMA, offset, vaddr, size, entry_id, 0, 0);

I'm not sure how you make emmc/usb/gmac's dma ctrl desc work around
without pbmt when they don't have cache coherency protocol. Do you
need to inject dma_sync for desc synchronization? What's the effect of
dynamic PMA in the patch series?

Thx.

>
> > Here is the Linux dma type to Svpbmt map:
> > PMA -> Normal
> > IO -> ioremap, pgprot_noncached
> > NC -> pgprot_writecombine
> >
> > How about AX45MP?
> >
> Svpbmt extension is not supported on AX45MP (reported by
> riscv_isa_extension_available())
>
> Cheers,
> Prabhakar



-- 
Best Regards
 Guo Ren