Re: [PATCH] i2c: imx: increase retries on arbitration loss

From: Oleksij Rempel <o.rempel@pengutronix.de>
To: Primoz Fiser <primoz.fiser@norik.com>
Cc: Marco Felsch <m.felsch@pengutronix.de>,
	Oleksij Rempel <linux@rempel-privat.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, upstream@lists.phytec.de
Subject: Re: [PATCH] i2c: imx: increase retries on arbitration loss
Date: Fri, 16 Dec 2022 12:02:27 +0100	[thread overview]
Message-ID: <20221216110227.GA12327@pengutronix.de> (raw)
In-Reply-To: <bb4882a9-8be6-5255-6256-aa1253362e59@norik.com>

On Fri, Dec 16, 2022 at 11:41:08AM +0100, Primoz Fiser wrote:
> Hi Marco,
> 
> On 16. 12. 22 10:45, Marco Felsch wrote:
> > Hi Primoz,
> > 
> > On 22-12-16, Primoz Fiser wrote:
> > > By default, retries value is set to 0 (no retries). Set retries to more
> > > sensible value of 3 to allow i2c core to re-attempt transfer in case of
> > > i2c arbitration loss (i2c-imx returns -EAGAIN errno is such case).
> > 
> > apart the fact that the number of retries vary a lot and so the client
> > driver behaviour can vary a lot which is not good IMHO, why do you think
> > that 3 is a sufficient number?
> 
> IMHO it is better than leaving it at 0 (no retries)?
> 
> Setting it to sensible value like 3 will at least attempt to make transfer
> in case arbitration-loss occurs.
> 
> > 
> > If an arbitration loss happen, why do you think that retrying it 3 times
> > changes that?
> 
> I our case, setting retries to non-zero value solves issues with PMIC
> shutdown on phyboard-mira which in some rare cases fails with "Failed to
> shutdown (err =  -11)" (-EAGAIN).
> 
> To me it makes common sense retries is set to non-zero value especially for
> such rare conditions/situations.

https://lore.kernel.org/all/Ys1bw9zuIwWS+bqw@shikoro/

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