linux-kernel - Re: [PATCH 1/2] mailbox: switch to hrtimer for tx

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Message-ID: <CABb+yY2CRPZB0VNCJZyzW9wa+3MrjxPjML-Q4Ga0eHmsEUB2KQ@mail.gmail.com>
Date:	Fri, 24 Jul 2015 10:32:15 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Juri Lelli <Juri.Lelli@....com>
Subject: Re: [PATCH 1/2] mailbox: switch to hrtimer for tx_complete polling

On Wed, Jul 22, 2015 at 5:58 PM, Sudeep Holla <sudeep.holla@....com> wrote:

> we might end-up waiting
> for atleast a jiffy even though the response for that message from the
> remote is received via interrupt and processed in relatively smaller
> time granularity.
>
That is wrong.

 If the controller supports TX interrupt it should set txdone_irq,
which prevents polling i.e, controller driver calls mbox_chan_txdone.

 If the controller doesn't support TX interrupt but the client
receives some ack packet, then the client should set knows_txdone and
call mbox_client_txdone. Again you don't have to wait on polling.

 If there's neither TX interrupt nor some ack packet, only then it has
to rely on polling. In which case, I doubt if we can desire some
functionality that requires sub-jiffy notification of TX_done.

Thanks.
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