linux-kernel - Re: [PATCH v8 5/7] cache: Add L2 cache management for Andes AX45MP RISC-V core

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Date:   Wed, 12 Apr 2023 21:25:34 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Prabhakar <prabhakar.csengg@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Heiko Stuebner <heiko@...ech.de>, Guo Ren <guoren@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Samuel Holland <samuel@...lland.org>,
        linux-riscv@...ts.infradead.org, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v8 5/7] cache: Add L2 cache management for Andes AX45MP
 RISC-V core

On Wed, Apr 12, 2023 at 12:08:58PM +0100, Prabhakar wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...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@...00000 {
>             compatible = "shared-dma-pool";
>             reg = <0x0 0x58000000 0x0 0x08000000>;
>             no-map;
>             linux,dma-default;
>         };
>     };
> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> ---
> v7 -> v8
> * Dropped function pointer usage
> * Now exporting the functions for clean/inval/flush
> * Switched to using early_initcall instead of arch_initcall
> * Dropped entry for "include/cache" from MAINTAINERS
> * Dropped dependency of RISCV on AX45MP_L2_CACHE
> * Returning error in case of cache line mismatch

> * Renamed clean/inval/flush functions

I kinda screwed you with that request given Hellwig's NAK on the
function pointer based stuff. Ah well, I prefer matching the proposed
naming of the dma core to what RVI chose for the instructions.

Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>

I suppose this will need a resubmission once Arnd's stuff gets applied,
but I would like to see it have a run through the build bots etc.

Cheers,
Conor.

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