Date:   Thu, 12 May 2022 14:51:19 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Hannes Reinecke <hare@...e.de>
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>, Rob Herring <robh+dt@...nel.org>,
        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 Thu, May 12, 2022 at 08:19:34AM +0200, Hannes Reinecke wrote:
> On 5/12/22 01:17, 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.
> > +
> > +  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:
> > +    $ref: '/schemas/types.yaml#/definitions/uint32'
> > +    description:
> > +      Mask that indicates which ports the HBA supports. Useful if PI is not
> > +      programmed by the BIOS, which is true for some embedded SoC's.
> > +    maximum: 0x1f
> > +
> > +patternProperties:
> > +  "^sata-port@[0-9a-f]+$":
> > +    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
> > +
> > +required:
> > +  - reg
> > +  - interrupts
> > +
> > +additionalProperties: true
> > +
> > +...
> > diff --git a/Documentation/devicetree/bindings/ata/ahci-platform.yaml b/Documentation/devicetree/bindings/ata/ahci-platform.yaml
> > index 9304e4731965..76075d3c8987 100644
> > --- a/Documentation/devicetree/bindings/ata/ahci-platform.yaml
> > +++ b/Documentation/devicetree/bindings/ata/ahci-platform.yaml
> > @@ -36,8 +36,7 @@ select:
> >       - compatible
> >   allOf:
> > -  - $ref: "sata-common.yaml#"
> > -
> > +  - $ref: "ahci-common.yaml#"
> 

> What happened to 'sata-common.yaml' ?

Nothing. It's still relevant for some devices.

> Not needed anymore? Included via other means?

Included by the SATA-compatible devices. Mainly that schema is relevant
to the devices which aren't AHCI-compatible.

> 
> Please clarify.

sata-common.yaml is a common schema for the SATA devices (including
AHCI-devices), while ahci-common.yaml is a common schema for the
AHCI-compatible devices. So the later is more restrictive, than the
former one. The SATA DT-indings can be used by the
AHCI-incompatible devices for instance by the ones handled in the
drivers drivers/ata/sata_*.c. The AHCI DT-schema can be used by the
AHCI-enabled platforms like described in the LLDDs drivers/ata/ahci_*.
This means if your device is based on AHCI, then its bindings should
refer to the ahci-common.yaml schema and specify the platform-specific
DT-bindings: new properties and common properties constraints. If it
isn't AHCI-compatible but is a Serial ATA device, then it's bindings
should refer to the sata-common.yaml schema (which is much less
restrictive and defines just some small set of the properties).

For instance the brcm,sata-brcm.yaml DT-bindings can be converted to
using the ahci-common.yaml schema instead of the sata-common.yaml
schema, while the renesas,rcar-sata.yaml bindings can refer to the
sata-common.yaml schema thus for instance restricting the DT-node name
to be 'sata' for which in the current RCAR SATA bindings there is no
relevant constraints.

-Sergey

> 
> Cheers,
> 
> Hannes
> -- 
> Dr. Hannes Reinecke		           Kernel Storage Architect
> hare@...e.de			                  +49 911 74053 688
> SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
> HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

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