Re: [RFC PATCH v3 2/2] soc: renesas: Add L2 cache management for RZ/Five SoC

["Lad, Prabhakar" <prabhakar.csengg@gmail.com>]

Hi Geert,

On Tue, Nov 1, 2022 at 12:43 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Thu, Oct 20, 2022 at 12:02 AM Prabhakar <prabhakar.csengg@gmail.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@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
> >
> > This patch adds support to configure the memory attributes of the memory
> > regions as passed from the l2 cache node and exposes the cache management
> > ops.
> >
> > More info about PMA (section 10.3):
> > http://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
> >
> > This feature is based on the work posted [0] by Vincent Chen
> > <vincentc@andestech.com> for the Andes AndeStart RISC-V CPU.
> >
> > [0] https://lore.kernel.org/lkml/1540982130-28248-1-git-send-email-vincentc@andestech.com/
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
>
> Thanks for your patch!
>
> > --- a/arch/riscv/mm/dma-noncoherent.c
> > +++ b/arch/riscv/mm/dma-noncoherent.c
> > @@ -24,13 +24,25 @@ void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> >
> >         switch (dir) {
> >         case DMA_TO_DEVICE:
> > +#ifdef CONFIG_ERRATA_THEAD_CMO
> >                 ALT_CMO_OP(clean, vaddr, size, riscv_cbom_block_size);
> > +#elif CONFIG_AX45MP_L2_CACHE
>
> "#elif defined(CONFIG_AX45MP_L2_CACHE)" (everywhere)
>
> Else it may fail with:
>
>     error: "CONFIG_AX45MP_L2_CACHE" is not defined, evaluates to 0
> [-Werror=undef]
>
Agreed, thanks for pointing this out. Said that I plan to get rid of
these checks in the next version (only after getting around the
ALTERNATIVE() macro).

Cheers,
Prabhakar