Re: [PATCH] i2c: designware: deduce speed mode from device tree setting

[Mark Rutland]

On Tue, Aug 19, 2014 at 09:18:49PM +0100, atull@xxxxxxxxxxxxxxxxxxxxx wrote:
> From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> 
> Use the documented, but unimplemented "clock-frequency"
> Device Tree setting as a guide on whether to set the speed
> mode bits in DW_IC_CON to standard or fast i2c mode.
> 
> Previously, the driver was hardwired to fast mode.  Default
> to fast mode if the "clock-frequency" property is not present
> for backwards compatiblity.
> 
> Signed-off-by: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/i2c/busses/i2c-designware-platdrv.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index bc87733..18cd3d9 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -122,7 +122,8 @@ static int dw_i2c_probe(struct platform_device *pdev)
>  	struct dw_i2c_dev *dev;
>  	struct i2c_adapter *adap;
>  	struct resource *mem;
> -	int irq, r;
> +	int irq, r, ret, speed = DW_IC_CON_SPEED_FAST;
> +	u32 bus_rate;
>  
>  	irq = platform_get_irq(pdev, 0);
>  	if (irq < 0) {
> @@ -167,6 +168,11 @@ static int dw_i2c_probe(struct platform_device *pdev)
>  		of_property_read_u32(pdev->dev.of_node,
>  				     "i2c-scl-falling-time-ns",
>  				     &dev->scl_falling_time);
> +
> +		ret = of_property_read_u32(pdev->dev.of_node,
> +					   "clock-frequency", &bus_rate);
> +		if (!ret && (bus_rate <= 100000))
> +			speed = DW_IC_CON_SPEED_STD;

This looks a bit odd.

If the device only supports two particular speeds why do we accept any
other speed in the clock-frequency property? Surely we should at least
warn that something was off?

Thanks,
Mark

>  	}
>  
>  	dev->functionality =
> @@ -177,7 +183,7 @@ static int dw_i2c_probe(struct platform_device *pdev)
>  		I2C_FUNC_SMBUS_WORD_DATA |
>  		I2C_FUNC_SMBUS_I2C_BLOCK;
>  	dev->master_cfg =  DW_IC_CON_MASTER | DW_IC_CON_SLAVE_DISABLE |
> -		DW_IC_CON_RESTART_EN | DW_IC_CON_SPEED_FAST;
> +		DW_IC_CON_RESTART_EN | speed;
>  
>  	/* Try first if we can configure the device from ACPI */
>  	r = dw_i2c_acpi_configure(pdev);
> -- 
> 1.7.9.5
> 
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