linux-kernel - Re: [PATCH v2 1/2] i2c: ocores: increase poll timeout to total transfer timeout

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Message-ID: <a528cdb9c861b8fb97ab1a99901378908f2e0e89.camel@ew.tq-group.com>
Date: Thu, 09 Oct 2025 15:26:12 +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 v2 1/2] i2c: ocores: increase poll timeout to total
 transfer timeout

On Thu, 2025-10-09 at 15:20 +0200, Andrew Lunn wrote:
> On Thu, Oct 09, 2025 at 11:19:49AM +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.
> > 
> > The behavior in the regular case is unchanged, spinning for up to 1ms,
> > but the open-coded poll loop is replaced with read_poll_timeout_atomic()
> > as suggested by Andrew Lunn. In cases where 1ms is not sufficient,
> > read_poll_timeout() is used, allowing a total transfer time up to the
> > timeout set in struct i2c_adapter (defaulting to 1s, configurable through
> > the I2C_TIMEOUT ioctl).
> 
> Thanks
> 
> Did you test with CONFIG_DEBUG_ATOMIC_SLEEP enabled? I don't think it
> is an issue, but the old code could be used in atomic context because
> it never slept.

I did not, but there is only one call chain ocores_xfer_core ->
ocores_process_polling -> ocores_poll_wait -> ocores_wait, which is definitely
not used in atomic context (in IRQ mode, ocores_xfer_core calls
wait_event_timeout, which might_sleep()).

Best,
Matthias



> 
> Reviewed-by: Andrew Lunn <andrew@...n.ch>
> 
>     Andrew

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