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SubjectRe: [PATCH v3 04/22] firmware: arm_scmi: add basic driver infrastructure for SCMI
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On 04/10/17 11:59, Arnd Bergmann wrote:
> On Thu, Sep 28, 2017 at 3:11 PM, Sudeep Holla <sudeep.holla@arm.com> wrote:
>
>> +/**
>> + * struct scmi_msg_hdr - Message(Tx/Rx) header
>> + *
>> + * @id: The identifier of the command being sent
>> + * @protocol_id: The identifier of the protocol used to send @id command
>> + * @seq: The token to identify the message. when a message/command returns,
>> + * the platform returns the whole message header unmodified including
>> + * the token.
>> + */
>> +struct scmi_msg_hdr {
>> + u8 id;
>> + u8 protocol_id;
>> + u16 seq;
>> + u32 status;
>> + bool poll_completion;
>> +};
>
> Is this structure part of the protocol, or just part of the linux
> implementation?
> If this is in the protocol, you should not have a 'bool' member in there, which
> does not have a well-defined binary representation across architectures.
>

No, it's not part of specification just linux, added to support polling
based DVFS messages.

>> +/*
>> + * The SCP firmware providing SCM interface to OSPM and other agents must
>> + * execute only in little-endian mode as per SCMI specification, so any buffers
>> + * shared through SCMI should have their contents converted to little-endian
>> + */
>
> That is a very odd thing to put into a specification, are you sure it requires
> a specific runtime endian-mode? I would bet that it only requires the protocol
> to use little-endian data, so better describe it like that.
>

Right, my bad. Not sure where I copied that text from, but as you
mention specification just expects data to be in LE format.

[..]

>
>> +#if IS_REACHABLE(CONFIG_ARM_SCMI_PROTOCOL)
>> +int scmi_handle_put(const struct scmi_handle *handle);
>> +const struct scmi_handle *scmi_handle_get(struct device *dev);
>> +const struct scmi_handle *devm_scmi_handle_get(struct device *dev);
>
> IS_REACHABLE() can easily lead to confusion when the driver is
> a loadable module but never gets used by a built-in driver. Maybe use
> IS_ENABLED() here, and add a Kconfig symbol that other drivers
> can depend on if you want them to optionally use it, like:
>
> config MAYBE_ARM_SCMI_PROTOCOL
> default y if ARM_SCMI_PROTOCOL=n
> default ARM_SCMI_PROTOCOL

OK, will check, we may not need that yet.

--
Regards,
Sudeep

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