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SubjectRe: [PATCH 1/2] dt-bindings: mailbox : arm,mhuv2: Allow for more RX interrupts
On Wed, Mar 29, 2023 at 04:39:35PM +0100, Cristian Marussi wrote:
> The ARM MHUv2 Receiver block can indeed support more interrupts, up to the
> maximum number of available channels, but anyway no more than the maximum
> number of supported interrupt for an AMBA device.
>
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
> Cc: devicetree@vger.kernel.org
>
> .../devicetree/bindings/mailbox/arm,mhuv2.yaml | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml
> index a4f1fe63659a..5a57f4e2a623 100644
> --- a/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml
> +++ b/Documentation/devicetree/bindings/mailbox/arm,mhuv2.yaml
> @@ -69,10 +69,15 @@ properties:
>
> interrupts:
> description: |
> - The MHUv2 controller always implements an interrupt in the "receiver"
> - mode, while the interrupt in the "sender" mode was not available in the
> - version MHUv2.0, but the later versions do have it.
> - maxItems: 1
> + The MHUv2 controller always implements at least an interrupt in the
> + "receiver" mode, while the interrupt in the "sender" mode was not
> + available in the version MHUv2.0, but the later versions do have it.
> + In "receiver" mode, beside a single combined interrupt, there could be
> + multiple interrupts, up to the number of implemented channels but anyway
> + no more than the maximum number of interrupts potentially supported by
> + AMBA.
> + minItems: 1
> + maxItems: 9

I am not sure 9 is the correct value here. IIUC it is just what Linux defines
as AMBA_NR_IRQS. Looking at the history it was bumped from 2 to 9 for use
by PL330 DMA driver. I couldn't find anything to relate this 9 in any
AMBA or other related specification.

Ideally I would say we don't know what the max here. We just have a platform
implementing 2 interrupts now. Do we for with 2 for now and change it if some
new users require more in the future ?

I will leave that to the DT maintainers but 9 is simply random based on Linux
code so I would rather choose some other random number with a better reasoning
than 9 as AMBA code in the kernel is limiting it to 9.

--
Regards,
Sudeep

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