Date:   Tue, 24 May 2022 10:19:14 -0500
From:   Rob Herring <robh@...nel.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Jens Axboe <axboe@...nel.dk>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 02/23] dt-bindings: ata: ahci-platform: Detach common
 AHCI bindings

On Sun, May 22, 2022 at 06:02:47PM +0300, Serge Semin wrote:
> On Tue, May 17, 2022 at 02:10:55PM -0500, Rob Herring wrote:
> > On Thu, May 12, 2022 at 02:17:49AM +0300, Serge Semin wrote:
> > > In order to create a more sophisticated AHCI controller DT bindings let's
> > > divide the already available generic AHCI platform YAML schema into the
> > > platform part and a set of the common AHCI properties. The former part
> > > will be used to evaluate the AHCI DT nodes mainly compatible with the
> > > generic AHCI controller while the later schema will be used for more
> > > thorough AHCI DT nodes description. For instance such YAML schemas design
> > > will be useful for our DW AHCI SATA controller derivative with four clock
> > > sources, two reset lines, one system controller reference and specific
> > > max Rx/Tx DMA xfers size constraints.
> > > 
> > > Note the phys and target-supply property requirement is preserved in the
> > > generic AHCI platform bindings because some platforms can lack of the
> > > explicitly specified PHYs or target device power regulators.
> > > 
> > > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > > 
> > > ---
> > > 
> > > Folks, I don't really see why the phys/target-supply requirement has been
> > > added to the generic AHCI DT schema in the first place. Probably just to
> > > imply some meaning for the sub-nodes definition. Anyway in one of the
> > > further patches I am adding the DW AHCI SATA controller DT bindings which
> > > won't require having these properties specified in the sub-nodes, but will
> > > describe additional port-specific properties. That's why I get to keep the
> > > constraints in the ahci-platform.yaml schema instead of moving them to the
> > > common schema.
> > > 
> > > Changelog v2:
> > > - This is a new patch created after rebasing v1 onto the 5.18-rc3 kernel.
> > > 
> > > Changelog v3:
> > > - Replace Jens's email address with Damien's one in the list of the
> > >   schema maintainers. (@Damien)
> > > ---
> > >  .../devicetree/bindings/ata/ahci-common.yaml  | 117 ++++++++++++++++++
> > >  .../bindings/ata/ahci-platform.yaml           |  68 +---------
> > >  2 files changed, 123 insertions(+), 62 deletions(-)
> > >  create mode 100644 Documentation/devicetree/bindings/ata/ahci-common.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/ata/ahci-common.yaml b/Documentation/devicetree/bindings/ata/ahci-common.yaml
> > > new file mode 100644
> > > index 000000000000..620042ca12e7
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/ata/ahci-common.yaml
> > > @@ -0,0 +1,117 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/ata/ahci-common.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Common Properties for Serial ATA AHCI controllers
> > > +
> > > +maintainers:
> > > +  - Hans de Goede <hdegoede@...hat.com>
> > > +  - Damien Le Moal <damien.lemoal@...nsource.wdc.com>
> > > +
> > > +description:
> > > +  This document defines device tree properties for a common AHCI SATA
> > > +  controller implementation. It's hardware interface is supposed to
> > > +  conform to the technical standard defined by Intel (see Serial ATA
> > > +  Advanced Host Controller Interface specification for details). The
> > > +  document doesn't constitute a DT-node binding by itself but merely
> > > +  defines a set of common properties for the AHCI-compatible devices.
> > > +
> > > +select: false
> > > +
> > > +allOf:
> > > +  - $ref: sata-common.yaml#
> > > +
> > > +properties:
> > > +  reg:
> > > +    description:
> > > +      Generic AHCI registers space conforming to the Serial ATA AHCI
> > > +      specification.
> > > +
> > > +  reg-names:
> > > +    description: CSR space IDs
> > > +
> > > +  interrupts:
> > > +    description:
> > > +      Generic AHCI state change interrupt. Can be implemented either as a
> > > +      single line attached to the controller as a set of the dedicated signals
> > > +      for the global and particular port events.
> > > +
> > > +  clocks:
> > > +    description:
> > > +      List of all the reference clocks connected to the controller.
> > > +
> > > +  clock-names:
> > > +    description: Reference clocks IDs
> > > +
> > > +  resets:
> > > +    description:
> > > +      List of the reset control lines to reset the controller clock
> > > +      domains.
> > > +
> > > +  reset-names:
> > > +    description: Reset line IDs
> > > +
> > > +  power-domains:
> > > +    description:
> > > +      List of the power domain the AHCI controller being a part of.
> > 
> 
> > There's not really any point in listing all the above properties here, 
> > because they all have to be listed in the device specific schemas.
> 
> I agree with dropping the reset, clocks and power-related properties,
> but it would be good to somehow signify that at least one IRQ is
> required. Is it possible to somehow set such constraint with open
> upper bound? If currently it isn't what about setting minItems: 1 (one
> generic IRQ) and maxItems: 32 (in case of the per-port IRQs platform)?

required:
  - interrupts

> 
> Regarding the reg and reg-names properties. Some constraints are added
> in one of the next patches of this series (you have already noticed
> that).
> 
> > 
> > > +
> > > +  ahci-supply:
> > > +    description: Power regulator for AHCI controller
> > > +
> > > +  target-supply:
> > > +    description: Power regulator for SATA target device
> > > +
> > > +  phy-supply:
> > > +    description: Power regulator for SATA PHY
> > > +
> > > +  phys:
> > > +    description: Reference to the SATA PHY node
> > > +    maxItems: 1
> > > +
> > > +  phy-names:
> > > +    maxItems: 1
> > > +
> > > +  ports-implemented:
> > > +    $ref: '/schemas/types.yaml#/definitions/uint32'
> > > +    description:
> > > +      Mask that indicates which ports the HBA supports. Useful if PI is not
> > > +      programmed by the BIOS, which is true for some embedded SoC's.
> > > +    maximum: 0x1f
> > 
> 
> > The AHCI spec says there's a max of 32 ports, not 5.
> > 
> > https://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/serial-ata-ahci-spec-rev1-3-1.pdf
> 
> Right. The maximum constraint is dropped in the patch:
> [PATCH v3 03/23] dt-bindings: ata: ahci-platform: Clarify common AHCI props constraints
> 
> > 
> > > +
> > > +patternProperties:
> > > +  "^sata-port@[0-9a-f]+$":
> > > +    type: object
> > > +    description:
> > > +      It is optionally possible to describe the ports as sub-nodes so
> > > +      to enable each port independently when dealing with multiple PHYs.
> > > +
> > > +    properties:
> > > +      reg:
> > > +        description: AHCI SATA port identifier
> > > +        maxItems: 1
> > > +
> > > +      phys:
> > > +        description: Individual AHCI SATA port PHY
> > > +        maxItems: 1
> > > +
> > > +      phy-names:
> > > +        description: AHCI SATA port PHY ID
> > > +        maxItems: 1
> > > +
> > > +      target-supply:
> > > +        description: Power regulator for SATA port target device
> > > +
> > > +    required:
> > > +      - reg
> > > +
> > > +    additionalProperties: true
> > 
> 
> > If device specific bindings can add their own properties (as this 
> > allows), then all the common sata-port properties needs to be its own 
> > schema document. That way the device binding can reference it, define 
> > extra properties and set 'unevaluatedProperties: false'.
> > 
> 
> Could you please be more specific the way it is supposed to look? We
> have already got the sata-port@.* object defined in the sata-common.yaml
> super-schema. Here I just redefine it with more specific properties.

If you want an example, see spi-peripheral-props.yaml and the change 
that introduced it.

If properties are defined in multiple locations, we have to be able to 
combine all those schemas to a single (logical, not single file) schema 
to apply it. That's the only way all the disjoint properties can be 
evaluated.

> Is it ok if I moved the sata-port@.* properties in the "definitions"
> section of the sata-common.yaml and ahci-common.yaml schema and
> re-used them right in the common bindings and, if required, in the
> device-specific schema?

Yes, I guess. There's not really any advantage to doing that. A separate 
schema file is only a small amount of boilerplate.

> Please confirm that the next schema hierarchy is what you were talking
> about and it will be ok in this case:
> 
> > Documentation/devicetree/bindings/ata/sata-common.yaml:
> ...
> + patternProperties:
> +   "^sata-port@[0-9a-e]$":
> +     $ref: '#/definitions/sata-port'
> + 
> + definitions:

'$defs' is preferred over 'definitions'.

> +   sata-port:
> +     type: object
> +   
> +     properties:
> +       reg:
> +         minimum: 0

That's the default.

> + 
> +     additionalProperties: true

Drop this.

> 
> > Documentation/devicetree/bindings/ata/ahci-common.yaml:
> ...
> + patternProperties:
> +   "^sata-port@[0-9a-e]$":
> +     $ref: '#/definitions/ahci-port'
> + 
> + definitions:
> +   ahci-port:
> +     $ref: /schemas/ata/sata-common.yaml#/definitions/sata-port
> +     properties:
> +       reg:
> +         minimum: 0
> +         maximum: 31
> ...
> + 
> +     additionalProperties: true

Drop this.

> 
> > Documentation/devicetree/bindings/ata/snps,dwc-ahci.yaml:
> ...
> + patternProperties:
> +   "^sata-port@[0-9a-e]$":
> +     $ref: /schemas/ata/ahci-common.yaml#/definitions/ahci-port
> +     properties:
> +       reg:
> +         minimum: 0
> +         maximum: 7
> + 
> +       snps,tx-ts-max:
> +         $ref: /schemas/types.yaml#/definitions/uint32
> + 
> +       snps,rx-ts-max:
> +         $ref: /schemas/types.yaml#/definitions/uint32
> +
> +     unevaluatedProperties: true

This needs to be false. And this should work as the $ref issue is only 
for the top-level schema.

Rob

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