Re: [PATCH v5 6/6] soc: renesas: Add L2 cache management for RZ/Five SoC

Geert Uytterhoeven
2022-12-15T20:18:07Z

Hi Conor,

On Thu, Dec 15, 2022 at 8:54 PM Conor Dooley <conor@kernel.org> wrote:
> On Thu, Dec 15, 2022 at 05:46:42PM +0000, Lad, Prabhakar wrote:
> > On Thu, Dec 15, 2022 at 11:10 AM Geert Uytterhoeven
> > <geert@linux-m68k.org> wrote:
> > > On Thu, Dec 15, 2022 at 12:06 PM Lad, Prabhakar
> > > <prabhakar.csengg@gmail.com> wrote:
> > > > On Thu, Dec 15, 2022 at 10:36 AM Geert Uytterhoeven
> > > > <geert@linux-m68k.org> wrote:
> > > > > On Mon, Dec 12, 2022 at 12:58 PM Prabhakar <prabhakar.csengg@gmail.com> wrote:
> > > > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > > > >
> > > > > > I/O Coherence Port (IOCP) provides an AXI interface for connecting
> > > > > > external non-caching masters, such as DMA controllers. The accesses
> > > > > > from IOCP are coherent with D-Caches and L2 Cache.
> > > > > >
> > > > > > IOCP is a specification option and is disabled on the Renesas RZ/Five
> > > > > > SoC due to this reason IP blocks using DMA will fail.
> > > > > >
> > > > > > 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
> > > > > >
> > > > > > More info about PMA (section 10.3):
> > > > > > Link: http://www.andestech.com/wp-content/uploads/AX45MP-1C-Rev.-5.0.0-Datasheet.pdf
> > > > > >
> > > > > > As a workaround for SoCs with IOCP disabled CMO needs to be handled by
> > > > > > software. Firstly OpenSBI configures the memory region as
> > > > > > "Memory, Non-cacheable, Bufferable" and passes this region as a global
> > > > > > shared dma pool as a DT node. With DMA_GLOBAL_POOL enabled all DMA
> > > > > > allocations happen from this region and synchronization callbacks are
> > > > > > implemented to synchronize when doing DMA transactions.
> > > > > >
> > > > > > Example PMA region passes as a DT node from OpenSBI:
> > > > > > reserved-memory {
> > > > > > #address-cells = <2>;
> > > > > > #size-cells = <2>;
> > > > > > ranges;
> > > > > >
> > > > > > pma_resv0@58000000 {
> > > > > > compatible = "shared-dma-pool";
> > > > > > reg = <0x0 0x58000000 0x0 0x08000000>;
> > > > > > no-map;
> > > > > > linux,dma-default;
> > > > > > };
> > > > > > };
> > > > > >
> > > > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > > >
> > > > > Thanks for your patch!
> > > > >
> > > > > > arch/riscv/include/asm/cacheflush.h | 8 +
> > > > > > arch/riscv/include/asm/errata_list.h | 28 ++-
> > > > > > drivers/soc/renesas/Kconfig | 6 +
> > > > > > drivers/soc/renesas/Makefile | 2 +
> > > > > > drivers/soc/renesas/rzfive/Kconfig | 6 +
> > > > > > drivers/soc/renesas/rzfive/Makefile | 3 +
> > > > > > drivers/soc/renesas/rzfive/ax45mp_cache.c | 256 ++++++++++++++++++++++
> > > > >
> > > > > Given this touches arch/riscv/include/asm/, I don't think the
> > > > > code belongs under drivers/soc/renesas/.
> > > > >
> > > > Ok. Do you have any suggestions on where you want me to put this code?
> > >
> > > As it plugs into core riscv functionality, I think it should be under
> > > arch/riscv/.
> > > if the RISC-V maintainers object to that, another option is
> > > drivers/soc/andestech/ or (new) drivers/cache/
> > >
> > RISC-V maintainers had already made it clear to not to include vendor
> > specific stuff in the arch/riscv folder, so I'll consider putting this
> > into drivers/cache/ folder to sync with the bindings.
> >
> > Conor/Palmer - do you have any objections/suggestions?
>
> I'm not its maintainer so sorta moot what I say, but having drivers in
> arch/riscv makes little sense to me..
> Putting stuff in drivers/cache does sound like a good idea since the
> binding is going there too.
>
> The SiFive ccache driver is in drivers/soc and it was suggested to me
> this week that there's likely going to be a second SiFive cache driver
> at some point in the near future. Plus Microchip are going to have to
> add cache management stuff to the existing SiFive ccache driver.
> Having them be their own thing makes sense in my mind - especially since
> they're not tied to SoCs sold by Andes or SiFive.
>
> I had a quick, and I mean *quick* look through other soc drivers to see
> if there were any other cache controller drivers but nothing stood out
> to me. Maybe someone else has more of a clue there. Ditto for misc, had
> a look but nothing seemed obvious.

Usually they're under arch/:
$ git ls-files -- "arch/*cache*" | wc -l
148
$ git ls-files -- "drivers/*cache*" | wc -l
63

E.g. arch/arm/mm/cache-l2x0.c.

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds