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

Thu Sep 8 01:39:02 PDT 2022

Hi Conor, Atish,

What RISC-V devices you have?

Ours is RISC-V uniprocessor without IO Coherence Port.

Currently USB, ethernet, SDHI/eMMC doesn't work with standard
DMA api's.

On RISC-V world, how do we handle DMA api for uniprocessor without
IO Coherence Port?

Cheers,
Biju

> -----Original Message-----
> From: Conor.Dooley at microchip.com <Conor.Dooley at microchip.com>
> Sent: 08 September 2022 00:38
> To: atishp at atishpatra.org
> Cc: Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj at bp.renesas.com>;
> paul.walmsley at sifive.com; palmer at dabbelt.com; aou at eecs.berkeley.edu;
> atishp at rivosinc.com; apatel at ventanamicro.com; geert+renesas at glider.be;
> linux-riscv at lists.infradead.org; linux-renesas-soc at vger.kernel.org;
> linux-kernel at vger.kernel.org; prabhakar.csengg at gmail.com; Biju Das
> <biju.das.jz at bp.renesas.com>
> Subject: Re: [RFC PATCH 1/2] riscv: vendors: andes: Add support to
> configure the PMA regions
> 
> On 07/09/2022 22:52, Atish Patra wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know
> > the content is safe
> >
> >
> > On Tue, Sep 6, 2022 at 3:40 AM <Conor.Dooley at microchip.com
> > <mailto:Conor.Dooley at microchip.com>> wrote:
> >
> > 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://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs
> > .kernel.org%2Friscv%2Fpatch-acceptance.html&data=05%7C01%7Cbiju.da
> > s.jz%40bp.renesas.com%7C7fd3275accdb450e547a08da912a0042%7C53d82571da1
> > 947e49cb4625a166a4a2a%7C0%7C0%7C637981906834865446%7CUnknown%7CTWFpbGZ
> > sb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3
> > D%7C3000%7C%7C%7C&sdata=YAV2Ahz7TFMJJ3wCj%2FAdDuDEcPq0kXXL%2B3o6FA
> > d0%2BUI%3D&reserved=0
> > <https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoc
> > s.kernel.org%2Friscv%2Fpatch-acceptance.html&data=05%7C01%7Cbiju.d
> > as.jz%40bp.renesas.com%7C7fd3275accdb450e547a08da912a0042%7C53d82571da
> > 1947e49cb4625a166a4a2a%7C0%7C0%7C637981906834865446%7CUnknown%7CTWFpbG
> > Zsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%
> > 3D%7C3000%7C%7C%7C&sdata=YAV2Ahz7TFMJJ3wCj%2FAdDuDEcPq0kXXL%2B3o6F
> > Ad0%2BUI%3D&reserved=0>
> >
> > 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.
> >
> >
> > It covers the standard SBI extensions as well. However, I don't think
> > this includes a vendor extension as there is no freeze or ratification
> > associated with vendor extensions.
> >
> > It would be good to discuss the policy around vendor SBI extensions
> > during LPC as well. We also need to discuss the ACPI policy as well.
> > We most likely need a BoF to discuss these adhoc topics. I will check
> > if we can schedule a BoF in advance.
> 
> I did briefly mention this to Palmer on IRC last night, just was busy
> today & didn't get a chance to reply here. The indication there was that
> yes, this paragraph did cover SBI extensions - which would make vendor
> extensions not permitted upstream.
> 
> We (microchip) are "only" doing a few ecalls in a driver but this seems a
> fair bit more intrusive since it is in arch code. Even if the answer is a
> "no" - a no from the horses mouth rather than on IRC & maybe some
> rewording of that doc to be clearer would be nice.
> 
> I'd be down for a BoF, even if just to get a "no" in person haha
> 
> Conor.
> 
> >
> > 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://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith
> > ub.com%2Flinux4microchip%2Flinux%2Fblob%2Flinux-5.15-mchp%2Fdrivers%2F
> > mailbox%2Fmailbox-miv-ihc.c%23L27&data=05%7C01%7Cbiju.das.jz%40bp.
> > renesas.com%7C7fd3275accdb450e547a08da912a0042%7C53d82571da1947e49cb46
> > 25a166a4a2a%7C0%7C0%7C637981906834865446%7CUnknown%7CTWFpbGZsb3d8eyJWI
> > joiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7
> > C%7C%7C&sdata=seNiuv6EsY1u0SIT33%2F0CWHJu401d5zSaNmVb%2BUHKPM%3D&a
> > mp;reserved=0
> > <https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit
> > hub.com%2Flinux4microchip%2Flinux%2Fblob%2Flinux-5.15-mchp%2Fdrivers%2
> > Fmailbox%2Fmailbox-miv-ihc.c%23L27&data=05%7C01%7Cbiju.das.jz%40bp
> > .renesas.com%7C7fd3275accdb450e547a08da912a0042%7C53d82571da1947e49cb4
> > 625a166a4a2a%7C0%7C0%7C637981906834865446%7CUnknown%7CTWFpbGZsb3d8eyJW
> > IjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%
> > 7C%7C%7C&sdata=seNiuv6EsY1u0SIT33%2F0CWHJu401d5zSaNmVb%2BUHKPM%3D&
> > amp;reserved=0>
> >
> >  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?
> >
> > Thanks, Conor.
> >
> >
> > _______________________________________________ linux-riscv mailing
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> >
> >
> >
> > -- Regards, Atish