linux-kernel - Re: [PATCH v5 3/3] i2c: imx: Don't generate STOP condition if arbitration has been lost

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Message-ID: <20201009081425.GD817@pengutronix.de>
Date:   Fri, 9 Oct 2020 10:14:25 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Christian Eggers <ceggers@...i.de>
Cc:     Oleksij Rempel <linux@...pel-privat.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        David Laight <David.Laight@...LAB.COM>,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        stable@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH v5 3/3] i2c: imx: Don't generate STOP condition if
 arbitration has been lost

On Wed, Oct 07, 2020 at 10:45:24AM +0200, Christian Eggers wrote:
> If arbitration is lost, the master automatically changes to slave mode.
> I2SR_IBB may or may not be reset by hardware. Raising a STOP condition
> by resetting I2CR_MSTA has no effect and will not clear I2SR_IBB.
> 
> So calling i2c_imx_bus_busy() is not required and would busy-wait until
> timeout.
> 
> Signed-off-by: Christian Eggers <ceggers@...i.de>
> Tested (not extensively) on Vybrid VF500 (Toradex VF50):
> Tested-by: Krzysztof Kozlowski <krzk@...nel.org>
> Cc: stable@...r.kernel.org # Requires trivial backporting, simple remove
>                            # the 3rd argument from the calls to
>                            # i2c_imx_bus_busy().

Acked-by: Oleksij Rempel <o.rempel@...gutronix.de>
Thank you!

> ---
>  drivers/i2c/busses/i2c-imx.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 63575af41c09..5d8a79319b2b 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -615,6 +615,8 @@ static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx, bool atomic)
>  		/* Stop I2C transaction */
>  		dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>  		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> +		if (!(temp & I2CR_MSTA))
> +			i2c_imx->stopped = 1;
>  		temp &= ~(I2CR_MSTA | I2CR_MTX);
>  		if (i2c_imx->dma)
>  			temp &= ~I2CR_DMAEN;
> @@ -778,9 +780,12 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx,
>  		 */
>  		dev_dbg(dev, "<%s> clear MSTA\n", __func__);
>  		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> +		if (!(temp & I2CR_MSTA))
> +			i2c_imx->stopped = 1;
>  		temp &= ~(I2CR_MSTA | I2CR_MTX);
>  		imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> -		i2c_imx_bus_busy(i2c_imx, 0, false);
> +		if (!i2c_imx->stopped)
> +			i2c_imx_bus_busy(i2c_imx, 0, false);
>  	} else {
>  		/*
>  		 * For i2c master receiver repeat restart operation like:
> @@ -905,9 +910,12 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs,
>  				dev_dbg(&i2c_imx->adapter.dev,
>  					"<%s> clear MSTA\n", __func__);
>  				temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
> +				if (!(temp & I2CR_MSTA))
> +					i2c_imx->stopped =  1;
>  				temp &= ~(I2CR_MSTA | I2CR_MTX);
>  				imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
> -				i2c_imx_bus_busy(i2c_imx, 0, atomic);
> +				if (!i2c_imx->stopped)
> +					i2c_imx_bus_busy(i2c_imx, 0, atomic);
>  			} else {
>  				/*
>  				 * For i2c master receiver repeat restart operation like:
> -- 
> Christian Eggers
> Embedded software developer
> 
> Arnold & Richter Cine Technik GmbH & Co. Betriebs KG
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> 
> 
> _______________________________________________
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> 

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