linux-kernel - RE: [PATCH v3 1/3] i2c: imx: Fix reset of I2SR

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Message-ID: <f8f1a9f54e0e426dbe27cc13a3b9de8d@AcuMS.aculab.com>
Date:   Tue, 6 Oct 2020 12:06:36 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christian Eggers' <ceggers@...i.de>,
        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>
CC:     Pengutronix Kernel Team <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v3 1/3] i2c: imx: Fix reset of I2SR_IAL flag

From: Christian Eggers
> Sent: 06 October 2020 11:52
> 
> According to the "VFxxx Controller Reference Manual" (and the comment
> block starting at line 97), Vybrid requires writing a one for clearing
> an interrupt flag. Syncing the method for clearing I2SR_IIF in
> i2c_imx_isr().
> 
> Signed-off-by: Christian Eggers <ceggers@...i.de>
> Cc: stable@...r.kernel.org
> ---
>  drivers/i2c/busses/i2c-imx.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 0ab5381aa012..745f4071155a 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -412,6 +412,19 @@ static void i2c_imx_dma_free(struct imx_i2c_struct *i2c_imx)
>  	dma->chan_using = NULL;
>  }
> 
> +static void i2c_imx_clear_irq(struct imx_i2c_struct *i2c_imx, unsigned int bits)
> +{
> +	unsigned int temp;
> +
> +	/*
> +	 * i2sr_clr_opcode is the value to clear all interrupts.
> +	 * Here we want to clear only <bits>, so we write
> +	 * ~i2sr_clr_opcode with just <bits> toggled.
> +	 */
> +	temp = ~i2c_imx->hwdata->i2sr_clr_opcode ^ bits;
> +	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2SR);
> +}

That looks either wrong or maybe just overcomplicated.
Why isn't:
	imx_i2c_write_reg(bits, i2c_imx, IMX_I2C_I2SR);
enough?

More usually you just write back the read value of such
'write 1 to clear' status registers and then act on all
the set bits.
That ensures you clear all interrupts that were pending.

If you need to avoid writes of bits that aren't in the
'clear all interrupts' value then you just need:
	bits &= i2c_imx->hwdata->i2sr_clr_opcode;
prior to the write.

	David

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