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

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Date:   Thu, 2 Nov 2017 12:37:22 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        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 02/11/17 12:21, Jassi Brar wrote:
> 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?
> 

I just said its *non-zero value* to give example. What action needs to
be done to trigger the doorbell is *entirely* controller specific and
typically it's a bit in the register.

>>
>> 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.
> 

I am *not* saying we will break other 10 controllers. All I am says
there are 4 controllers that can make use of this new feature. 4 is good
number IMO to generalize something.

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

Sure, it's working fine doesn't mean it can't be used at all. That's not
a right argument TBH.

-- 
Regards,
Sudeep