linux-kernel - Re: [PATCH v2 1/4] i2c: imx: only poll for bus busy in multi master mode

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Message-ID: <ZsYGbN36jwxyMAvE@eichest-laptop>
Date: Wed, 21 Aug 2024 17:23:24 +0200
From: Stefan Eichenberger <eichest@...il.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Fabio Estevam <festevam@...il.com>, kernel@...gutronix.de,
	andi.shyti@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
	Frank.Li@....com, francesco.dolcini@...adex.com,
	linux-i2c@...r.kernel.org, imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH v2 1/4] i2c: imx: only poll for bus busy in multi master
 mode

Hi Fabio, Oleksij,

On Wed, Aug 21, 2024 at 04:39:39PM +0200, Oleksij Rempel wrote:
> Hi Fabio, Stefan,
> 
> On Wed, Aug 21, 2024 at 08:01:20AM -0300, Fabio Estevam wrote:
> > Hi Stefan,
> > 
> > On Mon, Aug 19, 2024 at 4:20 AM Stefan Eichenberger <eichest@...il.com> wrote:
> > >
> > > From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > >
> > > According to the i.MX8M Mini reference manual chapter "16.1.4.2
> > > Generation of Start" it is only necessary to poll for bus busy and
> > > arbitration lost in multi master mode. This helps to avoid rescheduling
> > > while the i2c bus is busy and avoids SMBus devices to timeout.
> > >
> > > Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> > > Reviewed-by: Frank Li <Frank.Li@....com>
> > 
> > This fixes a pca953x probe error on an imx8mp board running linux-stable 6.6:
> > 
> > [    1.893260] pca953x 2-0020: failed writing register
> > [    1.898258] pca953x 2-0020: probe with driver pca953x failed with error -11
> > 
> > Could you please add a Fixes tag and Cc stable so that this can reach
> > the stable kernels?
> > 
> > Tested-by: Fabio Estevam <festevam@...x.de>

Thanks a lot for testing. Are the other patches required as well or did
only introducing the master mode flag solve the issue?

> > 
> > Thanks a lot,
> 
> It looks like with this patch, the I2SR_IAL interrupt is not cleared.
> I would expect some kind of interrupt storm. Can you confirm it?

This is a good question. i2c_imx_trx_complete was never called in the
interrupt handler. So that would mean the storm would already be there
before just for a shorter time. We only clear the IFF flag in the isr.

> This causes a processor interrupt request (if the interrupt enable is
> asserted [IIEN = 1]). The interrupt is set when one of the following
> occurs:
> - One byte transfer is completed (the interrupt is set at the falling
>   edge of the ninth clock).
> - An address is received that matches its own specific address in
>   Slave Receive mode.
> - Arbitration is lost.

Unfortunately, I don't have a device that uses multi master mode and we
would only see it on such a device. However, also from the reference
manual:

> IAL must be cleared by software by writing a "0" to it at the start of
> the interrupt service routine

So most likely it was wrong the whole the time we just didn't see it
before, could that be? I think a fix would be relatively easy we have to
clear it at the beginning of the isr but after we read the status. I
could add this to the series if you agree.

Regards,
Stefan