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

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Message-ID: <20221103032051.GD459441-robh@kernel.org>
Date:   Wed, 2 Nov 2022 22:20:51 -0500
From:   Rob Herring <robh@...nel.org>
To:     Conor Dooley <conor@...nel.org>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <anup@...infault.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [RFC PATCH v3 2/2] soc: renesas: Add L2 cache management for
 RZ/Five SoC

On Fri, Oct 21, 2022 at 11:32:01PM +0100, Conor Dooley wrote:
> On Fri, Oct 21, 2022 at 11:05:40PM +0100, Lad, Prabhakar wrote:
> > Hi Rob,
> > 
> > Thank you for the review.
> > 
> > On Fri, Oct 21, 2022 at 3:05 AM Rob Herring <robh@...nel.org> wrote:
> > >
> > > On Wed, Oct 19, 2022 at 11:02:42PM +0100, Prabhakar wrote:
> > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...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@...estech.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@...renesas.com>
> > > > ---
> > > >  arch/riscv/include/asm/cacheflush.h    |   8 +
> > > >  arch/riscv/include/asm/errata_list.h   |   2 +
> > > >  arch/riscv/mm/dma-noncoherent.c        |  20 ++
> > > >  drivers/soc/renesas/Kconfig            |   5 +
> > > >  drivers/soc/renesas/Makefile           |   4 +
> > > >  drivers/soc/renesas/rzf/Kconfig        |   6 +
> > > >  drivers/soc/renesas/rzf/Makefile       |   3 +
> > > >  drivers/soc/renesas/rzf/ax45mp_cache.c | 431 +++++++++++++++++++++++++
> > >
> > > How many cache drivers do we have around now? I've seen a few bindings
> > > go by. I'm guessing it is time to stop putting the drivers in the
> > > drivers/soc/ dumping ground.
> > >
> > The main reason this driver is not in arch/riscv is that it has vendor
> > specific extensions. Due to this reason it was agreed during the LPC
> > that vendor specific extension should be maintained by SoC vendors and
> > was agreed that this can go into drivers/soc/renesas folder instead.
> 
> Does not in drivers/soc mean they need to go into arch/riscv?
> The outcome of the chat at the LPC BoF was more that the cache drivers
> themselves should not be be routed via the arch maintainers, no?

drivers/cache/ or something is what I'm suggesting starting. The first 
thing is probably making an inventory of how many we already have.

Rob