linux-kernel - Re: [PATCH 2/3] i2c:imx: Add an extra read at the end of an I2C slave read

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Message-ID: <20211110085856.GD12195@pengutronix.de>
Date:   Wed, 10 Nov 2021 09:58:57 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     minyard@....org
Cc:     Pengutronix Kernel Team <kernel@...gutronix.de>,
        linux-i2c@...r.kernel.org,
        Andrew Manley <andrew.manley@...lingtech.com>,
        linux-kernel@...r.kernel.org, Corey Minyard <cminyard@...sta.com>
Subject: Re: [PATCH 2/3] i2c:imx: Add an extra read at the end of an I2C
 slave read

On Mon, Oct 04, 2021 at 07:32:15PM -0500, minyard@....org wrote:
> From: Corey Minyard <cminyard@...sta.com>
> 
> The I2C slave interface expects that the driver will read ahead one
> byte.  The IMX driver/device doesn't do this, but simulate it so that
> read operations get their index set correctly.
> 
> Signed-off-by: Corey Minyard <minyard@....org>
> Tested-by: Andrew Manley <andrew.manley@...lingtech.com>
> Reviewed-by: Andrew Manley <andrew.manley@...lingtech.com>

Reviewed-by: Oleksij Rempel <o.rempel@...gutronix.de>

> ---
>  drivers/i2c/busses/i2c-imx.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 97369fe48b30..26a04dc0590b 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -769,6 +769,15 @@ static irqreturn_t i2c_imx_slave_handle(struct imx_i2c_struct *i2c_imx,
>  		ctl &= ~I2CR_MTX;
>  		imx_i2c_write_reg(ctl, i2c_imx, IMX_I2C_I2CR);
>  		imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR);
> +
> +		/*
> +		 * The i2c slave interface requires one extra dummy
> +		 * read at the end to keep things in line.  See the
> +		 * I2C slave docs for details.
> +		 */
> +		i2c_imx_slave_event(i2c_imx,
> +				    I2C_SLAVE_READ_PROCESSED, &value);
> +
>  		i2c_imx_slave_finish_op(i2c_imx);
>  		return IRQ_HANDLED;
>  	}
> -- 
> 2.25.1
> 
> 

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