linux-kernel - Re: [PATCH v2 1/2] mailbox: add async request mechanism to empower controllers w/ hw queues

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Message-ID: <1df84f83-40d7-4719-a9f9-dfa10d25c667@linaro.org>
Date: Mon, 21 Oct 2024 07:18:07 +0100
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Jassi Brar <jassisinghbrar@...il.com>
Cc: krzk@...nel.org, alim.akhtar@...sung.com, mst@...hat.com,
 javierm@...hat.com, tzimmermann@...e.de, bartosz.golaszewski@...aro.org,
 luzmaximilian@...il.com, sudeep.holla@....com, conor.dooley@...rochip.com,
 bjorn@...osinc.com, ulf.hansson@...aro.org,
 linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, marcan@...can.st, neal@...pa.dev,
 alyssa@...enzweig.io, broonie@...nel.org, andre.draszik@...aro.org,
 willmcvicker@...gle.com, peter.griffin@...aro.org, kernel-team@...roid.com,
 vincent.guittot@...aro.org, daniel.lezcano@...aro.org
Subject: Re: [PATCH v2 1/2] mailbox: add async request mechanism to empower
 controllers w/ hw queues

Hi, Jassi,

On 10/18/24 8:49 AM, Tudor Ambarus wrote:
>>> The active request is considered completed when TX completes. But it seems
>>> that TX is not in direct relation with RX,
>>>
>> Correct, and it is not meant to be.
>> You are assuming there is always an RX in response to a TX, which is
> Not really. If there's no response expected, clients can set req->rx to
> NULL. Then the controllers know that no response is expected and can
> complete the request when TX completes.
> 
>> not the case. Many platforms just send a message and only need to know
>> when it is sent. Many platforms only listen for incoming messages.
> these 2 cases are covered with the req approach.
> 
>> Many platforms have TX and RX but not as parts of one exchange. In
> I don't think I understand this case. Is it related to what you describe
> below?
> 
>> fact, only minority of platforms expect RX after each TX. Btw, what if
> Right, I noticed.
> 
>> some platform sends only and always after each receive? For these
> This case is covered as well with the req approach. One just needs to
> serialize the requests:
> 
> ret = mbox_send_request(dc->mbox_chan, req1);
> ret = mbox_wait_request(ret, req1->wait);
> if (ret)
> 	return ret;
> 
> // req1 completed, send req2
> ret = mbox_send_request(dc->mbox_chan, req2);
> ret = mbox_wait_request(ret, req2->wait);
> if (ret)
> 	return ret;
> 	
> This shall work regardless if the client expects a response or not. If
> no response is expected, but just a TX completion, then the client can
> set req->rx = NULL.
> 
>> reasons, it is left to the user to tie an incoming RX to some previous
>> TX, or not.

Is there a specific driver that I can look at in order to understand the
case where RX is not tied to TX? It will speed me up a little.
Also, if you think there's a better way to enable controllers to manage
their hardware queues, please say.

Thanks,
ta