linux-kernel - Re: [PATCH 08/13] i2c: nomadik: replace jiffies by ktime for FIFO flushing timeout

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Message-Id: <CZ94S0SE0WFN.1RS0SY3KNMWQQ@bootlin.com>
Date: Mon, 19 Feb 2024 15:38:31 +0100
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Linus Walleij" <linus.walleij@...aro.org>
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 08/13] i2c: nomadik: replace jiffies by ktime for FIFO
 flushing timeout

Hello,

On Mon Feb 19, 2024 at 3:21 PM CET, Linus Walleij wrote:
> On Thu, Feb 15, 2024 at 5:52 PM Théo Lebrun <theo.lebrun@...tlin.com> wrote:
>
> > The FIFO flush function uses a jiffies amount to detect timeouts as the
> > flushing is async. Replace with ktime to get more accurate precision
> > and support short timeouts.
> >
> > Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
>
> Excellent patch. Thanks.
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

Somewhat related to this patch: while writing it, I noticed the total
timeout of flush_i2c_fifo() is 10 times the timeout. Without this
series, this means 10*200ms of busywaiting!

If you have an opinion on a more sensible option for this I could add a
patch to my V2. I don't know enough to pick a sensible value.

I'm unsure if it makes sense that the timeout of flush_i2c_fifo() is a
multiple of the transfer timeout. Does it make sense that those two
timeouts are correlated?

Big thanks for your review,

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