linux-kernel - Re: [PATCH 07/13] i2c: nomadik: support short xfer timeouts using waitqueue & hrtimer

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Message-ID: <CACRpkdYC=vVBA-s6GmsaED=NdXfsr0JDzzF+x8q8C3tqQ0F8YQ@mail.gmail.com>
Date: Mon, 19 Feb 2024 15:19:52 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Théo Lebrun <theo.lebrun@...tlin.com>
Cc: 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 07/13] i2c: nomadik: support short xfer timeouts using
 waitqueue & hrtimer

On Thu, Feb 15, 2024 at 5:52 PM Théo Lebrun <theo.lebrun@...tlin.com> 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.
>
> Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>

Part of me want to go and fix completions to handle hrtimer timeouts
for submicrosecond timeouts, BUT I realized that this is a bit thick
request for a simple driver, so just a suggestion for something we could
do one day. This is fine with me.
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij