Re: [PATCH 2/2] i2c-mux-gpio: eliminate i2c channel order assumptions

[Alexander Sverdlin]

Hi!

On 10/10/2013 10:39 AM, Ionut Nicu wrote:
> The i2c-mux driver uses the chan_id parameter provided
> in i2c_add_mux_adapter as a parameter to the select
> and deselect callbacks while the i2c-mux-gpio driver
> uses the chan_id as an index in the mux->data.values
> array.
> 
> A simple example of where this doesn't work is when we
> have a device tree like this:
> 
> i2cmux {
> 	i2c@1 {
> 		reg = <1>;
> 		...
> 	};
> 
> 	i2c@0 {
> 		reg = <0>;
> 		...
> 	};
> };
> 
> The mux->data.values array will be { 1, 0 }, but when
> the i2-mux driver will try to select channel 0, the
> i2c-mux-gpio driver will actually use values[0], hence 1
> as the gpio selection value.

The patch itself is correct, but the description is not precise,
I suppose... i2c-mux-gpio is consistent inside itself, it will
receive for every child adapter the value it has configured.
The problem happens inside i2c-mux.c, i2c_add_mux_adapter():

               	for_each_child_of_node(mux_dev->of_node, child) {
                       	ret = of_property_read_u32(child, "reg", &reg);
                       	if (ret)
                               	continue;
                       	if (chan_id == reg) {
                               	priv->adap.dev.of_node = child;

Which means, i2c-mux-gpio MUST pass reg, not its logical index inside
array. Otherwise node will not be correctly assigned and i2c-mux will
have problems selecting right adapter for the multiplexed devices.

> Signed-off-by: Ionut Nicu <ioan.nicu.ext@xxxxxxx>

So, for the code itself

Acked-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxx>

> ---
>  drivers/i2c/muxes/i2c-mux-gpio.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-mux-gpio.c b/drivers/i2c/muxes/i2c-mux-gpio.c
> index b5f17ef..3505d0e 100644
> --- a/drivers/i2c/muxes/i2c-mux-gpio.c
> +++ b/drivers/i2c/muxes/i2c-mux-gpio.c
> @@ -43,7 +43,7 @@ static int i2c_mux_gpio_select(struct i2c_adapter *adap, void *data, u32 chan)
>  {
>  	struct gpiomux *mux = data;
>  
> -	i2c_mux_gpio_set(mux, mux->data.values[chan]);
> +	i2c_mux_gpio_set(mux, chan);
>  
>  	return 0;
>  }
> @@ -233,7 +233,7 @@ static int i2c_mux_gpio_probe(struct platform_device *pdev)
>  		unsigned int class = mux->data.classes ? mux->data.classes[i] : 0;
>  
>  		mux->adap[i] = i2c_add_mux_adapter(parent, &pdev->dev, mux, nr,
> -						   i, class,
> +						   mux->data.values[i], class,
>  						   i2c_mux_gpio_select, deselect);
>  		if (!mux->adap[i]) {
>  			ret = -ENODEV;
> 

-- 
Best regards,
Alexander Sverdlin.
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