linux-kernel - Re: [PATCH v2 06/11] i2c: nomadik: support short xfer timeouts using waitqueue & hrtimer

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Message-Id: <CZKVXSULAGXC.1C5PDQJ6KCHN@bootlin.com>
Date: Mon, 04 Mar 2024 11:14:53 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Wolfram Sang" <wsa@...nel.org>
Cc: "Linus Walleij" <linus.walleij@...aro.org>, "Andi Shyti"
 <andi.shyti@...nel.org>, "Rob Herring" <robh+dt@...nel.org>, "Krzysztof
 Kozlowski" <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 <linux-arm-kernel@...ts.infradead.org>, <linux-i2c@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-mips@...r.kernel.org>, "Gregory Clement"
 <gregory.clement@...tlin.com>, "Vladimir Kondratiev"
 <vladimir.kondratiev@...ileye.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH v2 06/11] i2c: nomadik: support short xfer timeouts
 using waitqueue & hrtimer

Hello,

On Mon Mar 4, 2024 at 10:18 AM CET, Wolfram Sang wrote:
> On Thu, Feb 29, 2024 at 07:10:54PM +0100, Théo Lebrun wrote:
> > Replace the completion by a waitqueue for synchronization from IRQ
> > handler to task. For short timeouts, use hrtimers, else use timers.
> > Usecase: avoid blocking the I2C bus for too long when an issue occurs.
> > 
> > The threshold picked is one jiffy: if timeout is below that, use
> > hrtimers. This threshold is NOT configurable.
> > 
> > Implement behavior but do NOT change fetching of timeout. This means the
> > timeout is unchanged (200ms) and the hrtimer case will never trigger.
> > 
> > A waitqueue is used because it supports both desired timeout approaches.
> > See wait_event_timeout() and wait_event_hrtimeout(). An atomic boolean
> > serves as synchronization condition.
> > 
> > Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> > Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
>
> Largely:
>
> Reviewed-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Thanks for the reviews Wolfram.

> Nit:
>
> > -	int				timeout;
> > +	int				timeout_usecs;
>
> I think 'unsigned' makes a lot of sense here. Maybe u32 even?

Yes unsigned would make sense. unsigned int or u32, I wouldn't know
which to pick.

Regards,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com