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From: David Laight <David.Laight@ACULAB.COM>
To: "\'Christian Eggers\'" <ceggers@arri.de>,
	"Oleksij Rempel" <linux@rempel-privat.de>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Fabio Estevam" <festevam@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>,
	NXP Linux Team <linux-imx@nxp.com>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH v3 1/3] i2c: imx: Fix reset of I2SR_IAL flag
Date: Tue, 6 Oct 2020 12:06:36 +0000
Message-ID: <f8f1a9f54e0e426dbe27cc13a3b9de8d@AcuMS.aculab.com> (raw)
In-Reply-To: <20201006105135.28985-2-ceggers@arri.de>

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@arri.de>
> Cc: stable@vger.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

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-02 15:23 [PATCH v2 0/3] i2c: imx: Fix handling of arbitration loss Christian Eggers
2020-10-02 15:23 ` [PATCH v2 1/3] i2c: imx: Fix reset of I2SR_IAL flag Christian Eggers
2020-10-05  8:05   ` Krzysztof Kozlowski
2020-10-06  6:05   ` Uwe Kleine-König
2020-10-06 10:51     ` [PATCH v3 0/3] i2c: imx: Fix handling of arbitration loss Christian Eggers
2020-10-06 10:51       ` [PATCH v3 1/3] i2c: imx: Fix reset of I2SR_IAL flag Christian Eggers
2020-10-06 12:06         ` David Laight [this message]
2020-10-06 12:30           ` Christian Eggers
2020-10-06 12:46           ` Uwe Kleine-König
2020-10-06 12:52             ` David Laight
2020-10-06 10:51       ` [PATCH v3 2/3] i2c: imx: Check for I2SR_IAL after every byte Christian Eggers
2020-10-06 10:51       ` [PATCH v3 3/3] i2c: imx: Don't generate STOP condition if arbitration has been lost Christian Eggers
2020-10-02 15:23 ` [PATCH v2 2/3] i2c: imx: Check for I2SR_IAL after every byte Christian Eggers
2020-10-05  8:07   ` Krzysztof Kozlowski
2020-10-05  9:25     ` Christian Eggers
2020-10-02 15:23 ` [PATCH v2 3/3] i2c: imx: Don't generate STOP condition if arbitration has been lost Christian Eggers
2020-10-05  8:16   ` Krzysztof Kozlowski

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