linux-kernel - Re: [PATCH 2/3] dt-bindings: fpga: Add Efinix serial SPI programming binding description

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Date: Fri, 21 Jun 2024 10:11:24 +0200
From: Alexander Dahl <ada@...rsis.com>
To: Conor Dooley <conor@...nel.org>
Cc: iansdannapel@...il.com, mdf@...nel.org, hao.wu@...el.com,
	yilun.xu@...el.com, trix@...hat.com, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, linux-fpga@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: fpga: Add Efinix serial SPI programming
 binding description

Hello,

Am Thu, Jun 20, 2024 at 04:47:41PM +0100 schrieb Conor Dooley:
> On Thu, Jun 20, 2024 at 04:44:40PM +0200, iansdannapel@...il.com wrote:
> > From: Ian Dannapel <iansdannapel@...il.com>
> > 
> > Add device tree binding documentation for configuring Efinix FPGA
> > using serial SPI passive programming mode.
> > 
> > Signed-off-by: Ian Dannapel <iansdannapel@...il.com>
> > ---
> >  .../bindings/fpga/efnx,fpga-passive-spi.yaml  | 76 +++++++++++++++++++
> >  1 file changed, 76 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/fpga/efnx,fpga-passive-spi.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/fpga/efnx,fpga-passive-spi.yaml b/Documentation/devicetree/bindings/fpga/efnx,fpga-passive-spi.yaml
> > new file mode 100644
> > index 000000000000..855ceb3b89e8
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/fpga/efnx,fpga-passive-spi.yaml
> > @@ -0,0 +1,76 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/fpga/efnx,fpga-passive-spi.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Efinix SPI FPGA Manager
> > +
> > +description: |
> > +  Efinix Trion and Titanium Series FPGAs support a method of loading the
> > +  bitstream over what is referred to as "SPI Passive Programming".
> > +  Only serial (1x bus width) is supported, setting the programming mode
> > +  is not in the scope the this manager and must be done elsewhere.
> > +
> > +  References:
> > +  - https://www.efinixinc.com/docs/an033-configuring-titanium-fpgas-v2.6.pdf
> > +  - https://www.efinixinc.com/docs/an006-configuring-trion-fpgas-v6.0.pdf
> > +
> > +allOf:
> > +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - efnx,fpga-spi-passive
> 
> Ahh, here is the user. Can you please add specific compatibles for the
> Trion and Titanium series FPGAs? And when you do, make the filename
> match a compatible please.
> 
> Additionally, why "efnx" and not "efinix"?

FWIW, there already is "altr,fpga-passive-serial" for Altera devices.

Not sure why Altera got this short vendor prefix, but that was 2013
with commit 5db17a71a526 ("of: add vendor prefix for Altera Corp.")
and we probably never know?

The method of transferring the configuration data over SPI into the
FPGA is comparable.  I would go so far to claim a single driver could
support both device families for passive configuration over SPI.  I've
done that in a non-public driver for U-Boot few months ago, and used
"efinix,fpga-passive-serial" as a compatible there.  The difference is
basically Altera requiring more GPIOs considered, and Efinix keeping
the SPI clock on for some time after data is already transfered.

Greets
Alex

> 
> > +
> > +  spi-cpha: true
> > +  spi-cpol: true
> > +
> > +  spi-max-frequency:
> > +    maximum: 25000000
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  reset-gpios:
> > +    description:
> > +      reset pin (low active)
> > +    maxItems: 1
> > +
> > +  cs-gpios:
> > +    description:
> > +      chip-select pin (low active)
> > +    maxItems: 1
> > +
> > +  done-gpios:
> > +    description:
> > +      optional programming done pin, referred as CDONE (high active)
> 
> Why not call it "cdone-gpios" if that;s what it is referred to as?
> 
> > +    maxItems: 1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - reset-gpios
> > +  - cs-gpios
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    &spi2 {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      fpga_mgr_spi: fpga-mgr@0 {
> > +        compatible = "efnx,fpga-spi-passive";
> > +        spi-max-frequency = <25000000>;
> > +        spi-cpha;
> > +        spi-cpol;
> > +        reg = <0>;
> 
> order of compatible, reg, others here please.
> 
> > +        reset-gpios = <&gpio4 17 GPIO_ACTIVE_LOW>;
> > +        cs-gpios = <&gpio5 13 GPIO_ACTIVE_LOW>;
> > +        done-gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>;
> > +      };
> > +    };
> > +...
> > -- 
> > 2.34.1
> >