linux-kernel - RE: [RFC PATCH 1/2] riscv: vendors: andes: Add support to configure the PMA regions

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Date:   Wed, 7 Sep 2022 08:18:31 +0000
From:   Chris Paterson <Chris.Paterson2@...esas.com>
To:     "Conor.Dooley@...rochip.com" <Conor.Dooley@...rochip.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>
CC:     "atishp@...osinc.com" <atishp@...osinc.com>,
        "apatel@...tanamicro.com" <apatel@...tanamicro.com>,
        "geert+renesas@...der.be" <geert+renesas@...der.be>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "prabhakar.csengg@...il.com" <prabhakar.csengg@...il.com>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: RE: [RFC PATCH 1/2] riscv: vendors: andes: Add support to configure
 the PMA regions

Hello Conor,

Thank you for your interest.

> From: Conor.Dooley@...rochip.com <Conor.Dooley@...rochip.com>
> Sent: 06 September 2022 11:39
> 
> On 06/09/2022 11:21, Lad Prabhakar wrote:
> 
> > diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
> > index 2a0ef738695e..10a7c855d125 100644
> > --- a/arch/riscv/include/asm/sbi.h
> > +++ b/arch/riscv/include/asm/sbi.h
> > @@ -37,6 +37,7 @@ enum sbi_ext_id {
> >
> >          /* Vendor extensions must lie within this range */
> >          SBI_EXT_VENDOR_START = 0x09000000,
> > +       SBI_EXT_ANDES = 0x0900031E,
> >          SBI_EXT_VENDOR_END = 0x09FFFFFF,
> >   };
> 
> Everything else aside, I am very interested in what's happening
> here. I'll take a proper look through things later, but for now:
> 
> For PolarFire SoC we have an InterHart Communication SBI EXT that
> would would like to upstream support for. We are not aiming to put
> the driver itself in arch/riscv - it's just a mailbox driver, but
> I would like to use sbi.h for defining the vendor id etc.
> 
> I am not sure how this all aligns with:
> > We’ll only accept patches for new modules or extensions if the
> > specifications for those modules or extensions are listed as being
> > “Frozen” or “Ratified” by the RISC-V Foundation. (Developers may, of
> > course, maintain their own Linux kernel trees that contain code for
> > any draft extensions that they wish.)
> >
> > Additionally, the RISC-V specification allows implementors to create
> > their own custom extensions. These custom extensions aren’t required
> > to go through any review or ratification process by the RISC-V
> > Foundation. To avoid the maintenance complexity and potential
> > performance impact of adding kernel code for implementor-specific
> > RISC-V extensions, we’ll only to accept patches for extensions that
> > have been officially frozen or ratified by the RISC-V Foundation.
> > (Implementors, may, of course, maintain their own Linux kernel trees
> > containing code for any custom extensions that they wish.)
> 
> Which is in: https://docs.kernel.org/riscv/patch-acceptance.html
> 
> It is unclear to me whether that is just for ISA extensions or if that
> covers SBI extensions too. At least for us, since we don't touch arch
> code there is relatively little friction & there's no concerns about
> reducing the portability of a kernel since it is just a regular old
> driver.
> 
> I was planning on cornering some people *cough* Palmer *cough* at
> LPC and asking him what his thoughts were there.
> 
> FWIW this is what we have been doing:
> https://github.com/linux4microchip/linux/blob/linux-5.15-mchp/drivers/mailbox/mailbox-miv-ihc.c#L27
> 
> The IP itself has not stabilised yet, so we have not sent any patches
> yet, but we do intend doing so...
> 
> But yea, I'll take a properly look at what you're doing here soonTM,
> although at this point it may be the other side of LPC.
> 
> btw, where can I get my hands on your hardware?

The latest information I have is that it should be available via various distributors on the 21st Sept.

Kind regards, Chris

> 
> Thanks,
> Conor.
>