linux-kernel - Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue

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Date:   Fri, 21 Jul 2017 21:16:24 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Anup Patel <anup.patel@...adcom.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH v2 6/7] mailbox: bcm-flexrm-mailbox: Set msg_queue_len for
 each channel

Hi Anup,

On Fri, Jul 21, 2017 at 12:25 PM, Anup Patel <anup.patel@...adcom.com> wrote:
> The Broadcom FlexRM ring (i.e. mailbox channel) can handle
> larger number of messages queued in one FlexRM ring hence
> this patch sets msg_queue_len for each mailbox channel to
> be same as RING_MAX_REQ_COUNT.
>
> Signed-off-by: Anup Patel <anup.patel@...adcom.com>
> Reviewed-by: Scott Branden <scott.branden@...adcom.com>
> ---
>  drivers/mailbox/bcm-flexrm-mailbox.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mailbox/bcm-flexrm-mailbox.c b/drivers/mailbox/bcm-flexrm-mailbox.c
> index 9873818..20055a0 100644
> --- a/drivers/mailbox/bcm-flexrm-mailbox.c
> +++ b/drivers/mailbox/bcm-flexrm-mailbox.c
> @@ -1683,8 +1683,11 @@ static int flexrm_mbox_probe(struct platform_device *pdev)
>                 ret = -ENOMEM;
>                 goto fail_free_debugfs_root;
>         }
> -       for (index = 0; index < mbox->num_rings; index++)
> +       for (index = 0; index < mbox->num_rings; index++) {
> +               mbox->controller.chans[index].msg_queue_len =
> +                                               RING_MAX_REQ_COUNT;
>                 mbox->controller.chans[index].con_priv = &mbox->rings[index];
> +       }
>
While writing mailbox.c I wasn't unaware that there is the option to
choose the queue length at runtime.
The idea was to keep the code as simple as possible. I am open to
making it a runtime thing, but first, please help me understand how
that is useful here.

I understand FlexRm has a ring buffer of RING_MAX_REQ_COUNT(1024)
elements. Any message submitted to mailbox api can be immediately
written onto the ringbuffer if there is some space.
Is there any mechanism to report back to a client driver, if its
message in ringbuffer failed "to be sent"?
If there isn't any, then I think, in flexrm_last_tx_done() you should
simply return true if there is some space left in the rung-buffer,
false otherwise.

Thanks