RE: [EXT] Re: [PATCH v7 3/4] dt-bindings: irqchip: imx mu work as msi controller

[Frank Li <frank.li@nxp.com>]

> -----Original Message-----
> From: Marc Zyngier <maz@kernel.org>
> Sent: Friday, August 26, 2022 1:35 PM
> To: Frank Li <frank.li@nxp.com>
> Cc: Rob Herring <robh@kernel.org>; tglx@linutronix.de;
> krzysztof.kozlowski+dt@linaro.org; shawnguo@kernel.org;
> s.hauer@pengutronix.de; kw@linux.com; bhelgaas@google.com; linux-
> kernel@vger.kernel.org; devicetree@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-pci@vger.kernel.org; Peng Fan
> <peng.fan@nxp.com>; Aisheng Dong <aisheng.dong@nxp.com>;
> jdmason@kudzu.us; kernel@pengutronix.de; festevam@gmail.com; dl-linux-imx
> <linux-imx@nxp.com>; kishon@ti.com; lorenzo.pieralisi@arm.com;
> ntb@lists.linux.dev; lznuaa@gmail.com
> Subject: Re: [EXT] Re: [PATCH v7 3/4] dt-bindings: irqchip: imx mu work as msi
> controller
> 
> Caution: EXT Email
> 
> On Thu, 25 Aug 2022 22:42:38 +0100,
> Frank Li <frank.li@nxp.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Rob Herring <robh@kernel.org>
> > > Sent: Thursday, August 25, 2022 4:22 PM
> > > To: Frank Li <frank.li@nxp.com>
> > > Cc: maz@kernel.org; tglx@linutronix.de; krzysztof.kozlowski+dt@linaro.org;
> > > shawnguo@kernel.org; s.hauer@pengutronix.de; kw@linux.com;
> > > bhelgaas@google.com; linux-kernel@vger.kernel.org;
> > > devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux-
> > > pci@vger.kernel.org; Peng Fan <peng.fan@nxp.com>; Aisheng Dong
> > > <aisheng.dong@nxp.com>; jdmason@kudzu.us; kernel@pengutronix.de;
> > > festevam@gmail.com; dl-linux-imx <linux-imx@nxp.com>; kishon@ti.com;
> > > lorenzo.pieralisi@arm.com; ntb@lists.linux.dev; lznuaa@gmail.com
> > > Subject: [EXT] Re: [PATCH v7 3/4] dt-bindings: irqchip: imx mu work as msi
> > > controller
> > >
> > > Caution: EXT Email
> > >
> > > On Mon, Aug 22, 2022 at 10:51:29AM -0500, Frank Li wrote:
> > > > I.MX mu support generate irq by write a register. Provide msi controller
> > > > support so other driver such as PCI EP can use it by standard msi
> > > > interface as doorbell.
> > > >
> > > > Signed-off-by: Frank Li <Frank.Li@nxp.com>
> > > > ---
> > > >  .../interrupt-controller/fsl,mu-msi.yaml      | 98 +++++++++++++++++++
> > > >  1 file changed, 98 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/interrupt-
> > > controller/fsl,mu-msi.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/interrupt-
> controller/fsl,mu-
> > > msi.yaml b/Documentation/devicetree/bindings/interrupt-controller/fsl,mu-
> > > msi.yaml
> > > > new file mode 100644
> > > > index 0000000000000..ac07b138e24c0
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/interrupt-controller/fsl,mu-
> > > msi.yaml
> > > > @@ -0,0 +1,98 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id:
> > >
> https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicet
> > > ree.org%2Fschemas%2Finterrupt-controller%2Ffsl%2Cmu-
> > > msi.yaml%23&amp;data=05%7C01%7CFrank.Li%40nxp.com%7Cbff8f186128d
> > > 44209f4108da86dfc975%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0
> > > %7C637970592959950791%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLj
> > > AwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%
> > > 7C%7C&amp;sdata=DHCOhmaJAhwb8Gl%2FEbPj32B6lR2zcIvyMY%2BTuPACb
> > > zI%3D&amp;reserved=0
> > > > +$schema:
> > >
> https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicet
> > > ree.org%2Fmeta-
> > > schemas%2Fcore.yaml%23&amp;data=05%7C01%7CFrank.Li%40nxp.com%7
> > > Cbff8f186128d44209f4108da86dfc975%7C686ea1d3bc2b4c6fa92cd99c5c3016
> > > 35%7C0%7C0%7C637970592959950791%7CUnknown%7CTWFpbGZsb3d8eyJ
> > > WIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%
> > > 7C3000%7C%7C%7C&amp;sdata=J4znEXyHnMyQOssSUsoxE2Mlhe2qCDC%2F
> > > 9WN6SKv69aM%3D&amp;reserved=0
> > > > +
> > > > +title: Freescale/NXP i.MX Messaging Unit (MU) work as msi controller
> > > > +
> > > > +maintainers:
> > > > +  - Frank Li <Frank.Li@nxp.com>
> > > > +
> > > > +description: |
> > > > +  The Messaging Unit module enables two processors within the SoC to
> > > > +  communicate and coordinate by passing messages (e.g. data, status
> > > > +  and control) through the MU interface. The MU also provides the ability
> > > > +  for one processor (A side) to signal the other processor (B side) using
> > > > +  interrupts.
> > > > +
> > > > +  Because the MU manages the messaging between processors, the MU
> > > uses
> > > > +  different clocks (from each side of the different peripheral buses).
> > > > +  Therefore, the MU must synchronize the accesses from one side to the
> > > > +  other. The MU accomplishes synchronization using two sets of matching
> > > > +  registers (Processor A-facing, Processor B-facing).
> > > > +
> > > > +  MU can work as msi interrupt controller to do doorbell
> > > > +
> > > > +allOf:
> > > > +  - $ref: /schemas/interrupt-controller/msi-controller.yaml#
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    enum:
> > > > +      - fsl,imx6sx-mu-msi
> > > > +      - fsl,imx7ulp-mu-msi
> > > > +      - fsl,imx8ulp-mu-msi
> > > > +      - fsl,imx8ulp-mu-msi-s4
> > > > +
> > > > +  reg:
> > > > +    items:
> > > > +      - description: a side register base address
> > > > +      - description: b side register base address
> > > > +
> > > > +  reg-names:
> > > > +    items:
> > > > +      - const: processor a-facing
> > > > +      - const: processor b-facing
> > >
> > > Isn't 'a' and 'b' sufficient to distinguish? Personally, doesn't really
> > > look like a case that benefits from -names at all.
> > >
> > > In any case, -names shouldn't have spaces.
> >
> > I like "a" and "b".
> >
> > But Marc Zyngier suggested use above name.
> >
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spi
> nics.net%2Flists%2Flinux-
> pci%2Fmsg128783.html&amp;data=05%7C01%7Cfrank.li%40nxp.com%7Cadd154d
> 4aeda4059c93408da8791ba1b%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0
> %7C637971357205475355%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM
> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&a
> mp;sdata=vuaoWvu8BYcJ5NjOoUfFhlykBsW8vC2%2FbsrBmfx%2Bfz8%3D&amp;r
> eserved=0
> >
> > @Marc Zyngier
> 
> And I stand by my initial request. "a" doesn't convey any sort of
> useful information. Why not "I" and "II", while we're at it? Or
> something even funkier?

MU spec use term "a" and "b",  user have to map "I" an "II" to 
"a" and "b" when read MU spec and code. it is not straightforward.

I quote a part of spec. 
" The MU is connected as a peripheral under the Peripheral bus on both sides-on
the Processor A-side, the Processor A Peripheral Bus, and on the Processor B side,
the Processor B Peripheral Bus."

Rob Herring and Marc Zynginer:
I can change to any name, which you agree both. 

Some options:
1. "a", "b"
2. "a-side", "b-side"
3. "a-facing", "b-facing"
4. "I", "II"

> 
>         M.
> 
> --
> Without deviation from the norm, progress is not possible.