linux-kernel - Re: [PATCH 2/4] i2c: cadence: Set the hardware time-out register to maximum value

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Date:	Wed, 3 Dec 2014 12:28:30 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Harini Katakam <harinik@...inx.com>
Cc:	grant.likely@...aro.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, michal.simek@...inx.com,
	soren.brinkmann@...inx.com, linux-arm-kernel@...ts.infradead.org,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, vishnum@...inx.com
Subject: Re: [PATCH 2/4] i2c: cadence: Set the hardware time-out register to
 maximum value

On Tue, Dec 02, 2014 at 03:35:47PM +0530, Harini Katakam wrote:
> From: Vishnu Motghare <vishnum@...inx.com>
> 
> Cadence I2C controller has bug wherein it generates invalid read transactions
> after time-out in master receiver mode. This driver does not use the HW
> timeout and this interrupt is disabled but the feature itself cannot be
> disabled. Hence, this patch writes the maximum value (0xFF) to this register.
> This is one of the workarounds to this bug and it will not avoid the issue
> completely but reduce the chances of error.

This is a good description and should be in a comment in the driver.

> 
> Signed-off-by: Vishnu Motghare <vishnum@...inx.com>
> Signed-off-by: Harini Katakam <harinik@...inx.com>
> ---
>  drivers/i2c/busses/i2c-cadence.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index e54899e..8065205 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -111,6 +111,8 @@
>  #define CDNS_I2C_DIVA_MAX	4
>  #define CDNS_I2C_DIVB_MAX	64
>  
> +#define CDNS_I2C_TIMEOUT_MAX	0xFF
> +
>  #define cdns_i2c_readreg(offset)       readl_relaxed(id->membase + offset)
>  #define cdns_i2c_writereg(val, offset) writel_relaxed(val, id->membase + offset)
>  
> @@ -858,6 +860,8 @@ static int cdns_i2c_probe(struct platform_device *pdev)
>  		goto err_clk_dis;
>  	}
>  
> +	cdns_i2c_writereg(CDNS_I2C_TIMEOUT_MAX, CDNS_I2C_TIME_OUT_OFFSET);
> +
>  	dev_info(&pdev->dev, "%u kHz mmio %08lx irq %d\n",
>  		 id->i2c_clk / 1000, (unsigned long)r_mem->start, id->irq);
>  
> -- 
> 1.7.9.5
> 

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