linux-kernel - Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

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Date:   Thu, 2 Nov 2017 17:51:56 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH] mailbox: add support for doorbell/signal mode controllers

On Thu, Nov 2, 2017 at 5:19 PM, Sudeep Holla <sudeep.holla@....com> wrote:
> On 02/11/17 11:26, Jassi Brar wrote:

>>>> 1) Where does the  "whatever_value_to_trigger_signal"  come from?
>>>
>>> Controller specific.
>>>
>>>> That has to come from client.
>>>
>>> No.
>>>
>> Again, let me know what does the controller expect 'val' to be
>>
>>   writel(val, MAILBOX_A2B_CMD(chans->idx))
>>
>
> It depends on the controller. Whatever value that can generate a signal
> to remote.
>
As you _know_, the controller expects any non-zero value. Now what
value would you write in there?

>
> 1. pcc_send_data (drivers/mailbox/pcc.c)
> 2. sti_mbox_send_data (drivers/mailbox/mailbox-sti.c)
> 3. qcom_apcs_ipc_send_data (drivers/mailbox/qcom-apcs-ipc-mailbox.c)
> 4. tegra_hsp_doorbell_send_data (drivers/mailbox/tegra-hsp.c)
>
> And SCMI fits the above case.
>
These are only 4 out of 14. Can we overlook that your implementation
rules out 70% controllers.

BTW these 4 don't even need any send_signal() api, they would remain
unchanged. What's the new api for?