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

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Message-ID: <i5fkv3gx5mmegefc6ttydrwmsebozc6dcjzg7doc6vozjvekuv@hsn3mzobjggm>
Date: Thu, 22 Aug 2024 00:31:53 +0200
From: Andi Shyti <andi.shyti@...nel.org>
To: Stefan Eichenberger <eichest@...il.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, kernel@...gutronix.de, 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 Stefan,

On Wed, Aug 21, 2024 at 05:23:24PM GMT, Stefan Eichenberger wrote:
> On Wed, Aug 21, 2024 at 04:39:39PM +0200, Oleksij Rempel wrote:
> > On Wed, Aug 21, 2024 at 08:01:20AM -0300, Fabio Estevam wrote:
> > > On Mon, Aug 19, 2024 at 4:20 AM Stefan Eichenberger <eichest@...il.com> wrote:
> > > > 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?

The other patches don't need the Fix tag.

One question, does the issue happen with atomic transfers or any
transfers?

> > 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.

Please, if you can't test the patch don't send it.

Oleksij, I need your ack to apply this patch. What do you think
here?

Thanks,
Andi