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

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Message-ID: <ZeWRyuN8v-VnraQA@ninjato>
Date: Mon, 4 Mar 2024 10:18:02 +0100
From: Wolfram Sang <wsa@...nel.org>
To: Théo Lebrun <theo.lebrun@...tlin.com>
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

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>

Nit:

> -	int				timeout;
> +	int				timeout_usecs;

I think 'unsigned' makes a lot of sense here. Maybe u32 even?


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