Re: [PATCH 01/10] Documentation: dt-bindings: mailbox: tegra: Add binding for HSP mailbox

[Stephen Warren]

On 06/27/2016 03:02 AM, Joseph Lo wrote:
> Add DT binding for the Hardware Synchronization Primitives (HSP). The
> HSP is designed for the processors to share resources and communicate
> together. It provides a set of hardware synchronization primitives for
> interprocessor communication. So the interprocessor communication (IPC)
> protocols can use hardware synchronization primitive, when operating
> between two processors not in an SMP relationship.

This binding is quite different to the binding you sent to internal IP 
review. I wonder why it changed? Specific comments below:

> diff --git a/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt b/Documentation/devicetree/bindings/mailbox/nvidia,tegra186-hsp.txt

> +NVIDIA Tegra Hardware Synchronization Primitives (HSP)
> +
> +The HSP modules are used for the processors to share resources and communicate
> +together. It provides a set of hardware synchronization primitives for
> +interprocessor communication. So the interprocessor communication (IPC)
> +protocols can use hardware synchronization primitives, when operating between
> +two processors not in an SMP relationship.
> +
> +The features that HSP supported are shared mailboxes, shared semaphores,
> +arbitrated semaphores and doorbells.
> +
> +Required properties:
> +- name : Should be hsp
> +- compatible : Should be "nvidia,tegra<chip>-hsp"

I think this should explicitly list the value values of the compatible 
property, rather than being a generic/wildcard description:

- compatible
    Array of strings.
    One of:
  - "nvidia,tegra186-hsp"

If/when this binding supports other SoCs in the future, we'll add more 
entries into that list.

> +- reg : Offset and length of the register set for the device
> +- interrupts : Should contain the HSP interrupts
> +- interrupt-names: Should contain the names of the HSP interrupts that the
> +		   client are using.
> +		   "doorbell"

The binding should describe the HW, and not be affected by anything 
"that the client(s) are using". If there are multiple interrupts, we 
should list them all here, from the start.

When revising this, I would consider the following wording canonical:

- interrupt-names
    Array of strings.
    Contains a list of names for the interrupts described by the
    interrupts property. May contain the following entries, in any
    order:
    - "doorbell"
    - "..." (no doubt many more items will be listed here, e.g.
      for semaphores, etc.).
    Users of this binding MUST look up entries in the interrupts
    property by name, using this interrupts-names property to do so.
- interrupts
    Array of interrupt specifiers.
    Must contain one entry per entry in the interrupt-names property,
    in a matching order.

> +- nvidia,hsp-function : Specifies one of the HSP functions that the HSP unit
> +			will be supported. The function ID can be found in the
> +			header file <dt-bindings/mailbox/tegra-hsp.h>.

This property wasn't in the internal patch.

This doesn't make sense. The HW feature-set is fixed. This sounds like 
some kind of software configuration option, or a way to allow different 
drivers to handle different aspects of the HW? In general, the binding 
shouldn't be influenced by software structure. Please delete this property.

Now, if you're attempting to set up a binding where each function 
(semaphores, shared mailboxes, doorbells, etc.) has a different DT node, 
then (a) splitting up HW modules into sub-blocks has usually turned out 
to be a mistake in the past, and (b) the differences should likely be 
represented by using a different compatible property for each 
sub-component, rather than via a custom property.


The following properties were included in the internal patch:

                nvidia,num-SM = <0x8>;
                nvidia,num-AS = <0x2>;
                nvidia,num-SS = <0x2>;
                nvidia,num-DB = <0x7>;
                nvidia,num-SI = <0x8>;

... yet aren't here. True the compatible value implies those values; was 
that why the properties were removed?

> +Example:
> +
> +hsp_top: hsp@3c00000 {
...
> +bpmp@d0000000 {
> +	...
> +	mboxes = <&hsp_top HSP_DB_MASTER_BPMP>;
> +	...
> +};

I'd suggest not including the bpmp node in the example, since it's not 
part of the HSP node. If you do, recall that bpmp has no reg property 
and hence the node name shouldn't include a unit address.

> diff --git a/include/dt-bindings/mailbox/tegra-hsp.h b/include/dt-bindings/mailbox/tegra-hsp.h

This file should probably be named tegra186-hsp, since I doubt the 
master ID values will be stable between chips.

> +/*
> + * This header provides constants for binding nvidia,tegra<chip>-hsp.

That should say "186" not "<chip>"

> +#ifndef _DT_BINDINGS_MAILBOX_TEGRA186_HSP_H
> +#define _DT_BINDINGS_MAILBOX_TEGRA186_HSP_H

The two changes mentioned above would be consistent with that include 
guard's name including the text "186".

> +#define HSP_SHARED_MAILBOX		0
> +#define HSP_SHARED_SEMAPHORE		1
> +#define HSP_ARBITRATED_SEMAPHORE	2
> +#define HSP_DOORBELL			3

I think those should be removed, along with the nvidia,hsp-function 
property.