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Date:   Wed, 30 Mar 2022 09:48:44 -0500
From:   Rob Herring <robh@kernel.org>
To:     Dipen Patel <dipenp@nvidia.com>
Cc:     thierry.reding@gmail.com, jonathanh@nvidia.com,
        smangipudi@nvidia.com, linux-kernel@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-gpio@vger.kernel.org,
        linus.walleij@linaro.org, bgolaszewski@baylibre.com,
        warthog618@gmail.com, devicetree@vger.kernel.org,
        linux-doc@vger.kernel.org
Subject: Re: [PATCH v5 04/11] dt-bindings: Add HTE bindings
Message-ID: <YkRtzJjHQvmYNlK8@robh.at.kernel.org>
References: <20220329054521.14420-1-dipenp@nvidia.com>
 <20220329054521.14420-5-dipenp@nvidia.com>
 <YkOVgRBtXX0k9zr1@robh.at.kernel.org>
 <3b0f3430-bc1c-26df-c93f-517ba395d9e3@nvidia.com>
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On Tue, Mar 29, 2022 at 05:19:10PM -0700, Dipen Patel wrote:
> Hi,
> 
> On 3/29/22 4:25 PM, Rob Herring wrote:
> > On Mon, Mar 28, 2022 at 10:45:14PM -0700, Dipen Patel wrote:
> >> Introduces HTE devicetree binding details for the HTE subsystem. It
> >> includes examples for the consumers, binding details for the providers
> >> and specific binding details for the Tegra194 based HTE providers.
> >>
> >> Signed-off-by: Dipen Patel <dipenp@nvidia.com>
> >> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> >> ---
> >> Changes in v2:
> >> - Replace hte with hardware-timestamp for property names
> >> - Renamed file
> >> - Removed example from the common dt binding file.
> >>
> >> Changes in v3:
> >> - Addressed grammatical errors.
> >> - Removed double plural from the respective properties.
> >> - Added dual license.
> >> - Prefixed "nvidia" in nvidia specific properties.
> >>
> >> Changes in v4:
> >> - Corrected make dt_binding_check error.
> >>
> >> Changes in v5:
> >> - Addressed review comments.
> >>
> >>  .../hte/hardware-timestamps-common.yaml       | 29 +++++++
> >>  .../devicetree/bindings/hte/hte-consumer.yaml | 43 ++++++++++
> >>  .../bindings/hte/nvidia,tegra194-hte.yaml     | 82 +++++++++++++++++++
> >>  3 files changed, 154 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/hte/hardware-timestamps-common.yaml
> >>  create mode 100644 Documentation/devicetree/bindings/hte/hte-consumer.yaml
> >>  create mode 100644 Documentation/devicetree/bindings/hte/nvidia,tegra194-hte.yaml
> >>
> >> diff --git a/Documentation/devicetree/bindings/hte/hardware-timestamps-common.yaml b/Documentation/devicetree/bindings/hte/hardware-timestamps-common.yaml
> >> new file mode 100644
> >> index 000000000000..e8a69ceccd56
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/hte/hardware-timestamps-common.yaml
> >> @@ -0,0 +1,29 @@
> >> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> >> +%YAML 1.2
> >> +---
> >> +$id: https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fschemas%2Fhte%2Fhardware-timestamps-common.yaml%23&amp;data=04%7C01%7Cdipenp%40nvidia.com%7C5793b3be05fd48a97ad108da11db79a7%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637841931589163420%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=oyeG06oNMukYew%2Bkji%2FlXsDyGwIIrIvwxLHKxaiFBto%3D&amp;reserved=0
> >> +$schema: https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fmeta-schemas%2Fcore.yaml%23&amp;data=04%7C01%7Cdipenp%40nvidia.com%7C5793b3be05fd48a97ad108da11db79a7%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637841931589163420%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=JOY3MmZlMo6Mopr5dwjUky%2BaQX4b0QSiDt8zo3mSu1k%3D&amp;reserved=0
> >> +
> >> +title: Hardware timestamp providers
> >> +
> >> +maintainers:
> >> +  - Dipen Patel <dipenp@nvidia.com>
> >> +
> >> +description:
> >> +  Some devices/SoCs have hardware time stamping engines which can use hardware
> >> +  means to timestamp entity in realtime. The entity could be anything from
> >> +  GPIOs, IRQs, Bus and so on. The hardware timestamp engine (HTE) present
> >> +  itself as a provider with the bindings described in this document.
> >> +
> >> +properties:
> >> +  $nodename:
> >> +    pattern: "^hardware-timestamp(@.*|-[0-9a-f])?$"
> >> +
> >> +  "#hardware-timestamp-cells":
> >> +    description:
> >> +      Number of cells in a HTE specifier.
> >> +
> >> +required:
> >> +  - "#hardware-timestamp-cells"
> >> +
> >> +additionalProperties: true
> >> diff --git a/Documentation/devicetree/bindings/hte/hte-consumer.yaml b/Documentation/devicetree/bindings/hte/hte-consumer.yaml
> >> new file mode 100644
> >> index 000000000000..be69f63aa8c3
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/hte/hte-consumer.yaml
> >> @@ -0,0 +1,43 @@
> >> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> >> +%YAML 1.2
> >> +---
> >> +$id: https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fschemas%2Fhte%2Fhte-consumer.yaml%23&amp;data=04%7C01%7Cdipenp%40nvidia.com%7C5793b3be05fd48a97ad108da11db79a7%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637841931589319655%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=0f1FFB1IotZESaxDlXX5mo9YyMN25BlFAyq%2FOQJtVoE%3D&amp;reserved=0
> >> +$schema: https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdevicetree.org%2Fmeta-schemas%2Fcore.yaml%23&amp;data=04%7C01%7Cdipenp%40nvidia.com%7C5793b3be05fd48a97ad108da11db79a7%7C43083d15727340c1b7db39efd9ccc17a%7C0%7C0%7C637841931589319655%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=B%2FvVGGwp9JghUpT33cGk0EZHDRlaOAzCbtv93Z%2Fa9YY%3D&amp;reserved=0
> >> +
> >> +title: HTE Consumer Device Tree Bindings
> >> +
> >> +maintainers:
> >> +  - Dipen Patel <dipenp@nvidia.com>
> >> +
> >> +select: true
> >> +
> >> +description:
> >> +  HTE properties should be named "hardware-timestamps". The exact meaning of
> >> +  each hardware-timestamps property must be documented in the device tree
> > The meaning of the cells needs to be documented. You are documenting the 
> > meaning of 'hardware-timestamps' here.
> 
> This is for the consumer side, meaning of the cells will be documented in the provider
> 
> binding document.

Right cells are opaque to the consumer. What bothered me is 
hardware-timestamps already has an 'exact meaning'. You need to me more 
exact as to what should be documented. We don't want what 
'hardware-timestamps' is described again. What needs to be documented is 
how many entries, what each entry is (for the consumer), and the order.


> >> +  binding for each device. An optional property "hardware-timestamp-names" may
> >> +  contain a list of strings to label each of the HTE devices listed in the
> >> +  "hardware-timestamps" property.
> >> +
> >> +properties:
> >> +  hardware-timestamps:
> > I'm wondering if we should just drop 'hardware'. What other kind of 
> > timestamps are we going to have in DT? software-timestamps? No.
> 
> I believe this makes it explicit and leaves no room for second guess. If
> 
> only timestamps, ambiguity then will be which timestamp it is i.e. through hardware
> 
> engine, pps, ptp and so on...

Those aren't hardware timestamps, too? If those needed a similar 
binding, couldn't they use this binding? PTP at least is sometimes an 
separate, external chip IIRC.

Rob