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    SubjectRe: [PATCH 3/3] mailbox: Add support for ST's Mailbox IP
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    On Wed, Mar 18, 2015 at 6:47 PM, Lee Jones <lee.jones@linaro.org> wrote:
    > On Tue, 03 Mar 2015, Jassi Brar wrote:
    >
    >> On 3 March 2015 at 17:04, Arnd Bergmann <arnd@arndb.de> wrote:
    >> > On Tuesday 03 March 2015 10:41:23 Lee Jones wrote:
    >> >> +
    >> >> +/*
    >> >> + * struct sti_mbox_msg - sti mailbox message description
    >> >> + * @dsize: data payload size
    >> >> + * @pdata: message data payload
    >> >> + */
    >> >> +struct sti_mbox_msg {
    >> >> + u32 dsize;
    >> >> + u8 *pdata;
    >> >> +};
    >> >
    >> > As mentioned in another thread, we may just want to add a 'size'
    >> > argument to the message send function, and a default helper for
    >> > messages with size of 32 bits.
    >> >
    >> Case-a) 'size' is a member of the payload structure itself
    >> The extra 'size' argument would only be used for sanity check.
    >> This driver seems so. Lee, can you not do without 'dsize'?
    >>
    >> Case-b) 'size' is not a member of payload structure:
    >> b1) payload is fixed length, that is 'size' := sizeof(struct my_payload)
    >> Here the size argument is redundant.
    >>
    >> b2) payload length varies
    >> This case is highly unlikely because there would be no way
    >> for remote to know how many bytes to read as the payload. Not to mean
    >> we can't do without the 'size' argument.
    >>
    >> Your opinion has huge weight, but I would like to be enlightened
    >> before agreeing.
    >
    > Let's simplify this.
    >
    > If you want to have varying length payloads, you have to carry the
    > size in the payload. If you wish to force fixed size payloads, then
    > you may do without a size segment.
    >
    > Do you really want to force all users of Mailbox to use fixed size
    > payloads?
    >
    No. I only observed the fact that every known mailbox controller
    driver already has a way to figure out the payload length because
    either the protocol uses fixed length payloads or has the 'size' field
    in every payload.
    I am yet to see a platform that uses both, then the 'size' argument
    will be helpful but still not necessary.

    -Jassi


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