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

Thu Sep 8 05:43:00 PDT 2022

On 08/09/2022 09:39, Biju Das wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Hi Conor, Atish,
> 
> What RISC-V devices you have?

A bunch ;)

A __couple__ PolarFire SoC boards, HiFive Unleashed, D1 Nezha,
Canaan k210 MAIX something & the VisionFive.

> Ours is RISC-V uniprocessor without IO Coherence Port.

What does "IO Coherence Port" mean? Zicbo*?

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

Sounds pretty similar to the D1 so.

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

If you do mean Zicbo* you're into errata territory there & I don't
know if that'll be acceptable upstream - not for me to make that
call...

Thanks,
Conor.

> 
> 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:
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>>>
>>> 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
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>>> 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
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>>> 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
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>>> 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
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>>> 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.
>>>
>>>
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>>>
>>>
>>> -- Regards, Atish
> 