linux-kernel - Re: [PATCH 1/2] i2c: ocores: replace 1ms poll iteration timeout with total transfer timeout

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Message-ID: <09aa8945c41cdc0c518bddedf8d3489c1e521661.camel@ew.tq-group.com>
Date: Tue, 07 Oct 2025 16:06:36 +0200
From: Matthias Schiffer <matthias.schiffer@...tq-group.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Peter Korsgaard <peter@...sgaard.com>, Andi Shyti
 <andi.shyti@...nel.org>,  linux-i2c@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux@...tq-group.com
Subject: Re: [PATCH 1/2] i2c: ocores: replace 1ms poll iteration timeout
 with total transfer timeout

On Tue, 2025-10-07 at 14:34 +0200, Andrew Lunn wrote:
> On Tue, Oct 07, 2025 at 02:09:24PM +0200, Matthias Schiffer wrote:
> > When a target makes use of clock stretching, a timeout of 1ms may not be
> > enough. One extreme example is the NXP PTN3460 eDP to LVDS bridge, which
> > takes ~320ms to send its ACK after a flash command has been
> > submitted.
> > 
> > Replace the per-iteration timeout of 1ms with limiting the total
> > transfer time to the timeout set in struct i2c_adapter (defaulting to
> > 1s, configurable through the I2C_TIMEOUT ioctl). While we're at it, also
> > add a cpu_relax() to the busy poll loop.
> 
> 1s is a long time to spin. Maybe it would be better to keep with the
> current spin for 1ms, and then use one of the helpers from iopoll.h to
> do a sleeping wait? Say with 10ms sleeps, up to the 1s maximum?
> 
> 	Andrew

Makes sense. I don't think I can use something from iopoll.h directly, as i2c-
ocores has its own ioreadX abstraction to deal with different register widths
and endianesses, but a combination of spin + sleep is probably the way to go.

Best,
Matthias



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