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

Geert Uytterhoeven
2022-12-15T10:35:26Z

Hi Prabhakar,

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/.

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