linux-kernel - Re: [PATCH 1/3] i2c: imx: Fix reset of I2SR

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Message-ID: <16013235.tl8pWZfNaG@n95hx1g2>
Date:   Thu, 17 Sep 2020 16:13:50 +0200
From:   Christian Eggers <ceggers@...i.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
CC:     Oleksij Rempel <linux@...pel-privat.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH 1/3] i2c: imx: Fix reset of I2SR_IAL flag

Hello Uwe,

On Thursday, 17 September 2020, 16:02:35 CEST, Uwe Kleine-König wrote:
> Hello,
> 
> On Thu, Sep 17, 2020 at 02:20:27PM +0200, Christian Eggers wrote:
> ...
> >  		/* check for arbitration lost */
> >  		if (temp & I2SR_IAL) {
> >  			temp &= ~I2SR_IAL;
> > +			temp |= (i2c_imx->hwdata->i2sr_clr_opcode & I2SR_IAL);
> >  			imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2SR);
> >  			return -EAGAIN;
> ...

> This looks strange. First the flag is cleared and then it is (in some
> cases) set again.
i.MX controllers require writing a 0 to clear these bits. Vybrid controllers
need writing a 1 for the same.

> If I2SR_IIF is set in temp you ack this irq without handling it. (Which
> might happen if atomic is set and irqs are off?!)
This patch is only about using the correct processor specific value for 
acknowledging an IRQ... But I think that returning EAGAIN (which aborts the
transfer) should be handling enough. At the next transfer, the controller will
be set back to master mode.

> I see this idiom is used in a few more places in the driver already, I
> didn't check but these might have the same problem maybe?

Best regards
Christian