linux-kernel - Re: [PATCH RFC v3 3/4] mux: Add support for reading mux enable state from DT

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Date:   Tue, 30 Nov 2021 11:14:03 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Peter Rosin <peda@...ntia.se>
CC:     Vignesh Raghavendra <vigneshr@...com>, Nishanth Menon <nm@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-can@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH RFC v3 3/4] mux: Add support for reading mux enable state
 from DT

Hi Peter,

On 25/11/21 7:22 pm, Peter Rosin wrote:
> Hi!
> 
> On 2021-11-23 09:12, Aswath Govindraju wrote:
>> In some cases, we might need to provide the state of the mux to be set for
>> the operation of a given peripheral. Therefore, pass this information using
>> the second argument of the mux-controls property.
>>
>> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
>> ---
>>  drivers/mux/core.c           | 146 ++++++++++++++++++++++++++++++++++-
>>  include/linux/mux/consumer.h |  19 ++++-
>>  include/linux/mux/driver.h   |  13 ++++
>>  3 files changed, 173 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/mux/core.c b/drivers/mux/core.c
>> index 22f4709768d1..9622b98f9818 100644
>> --- a/drivers/mux/core.c
>> +++ b/drivers/mux/core.c
>> @@ -370,6 +370,29 @@ int mux_control_select_delay(struct mux_control *mux, unsigned int state,
>>  }
>>  EXPORT_SYMBOL_GPL(mux_control_select_delay);
>>  

[...]

>>  }
>>  
>>  /**
>> - * mux_control_get() - Get the mux-control for a device.
>> + * mux_get() - Get the mux-control for a device.
>>   * @dev: The device that needs a mux-control.
>>   * @mux_name: The name identifying the mux-control.
>> + * @enable_state: The variable to store the enable state for the requested device
>>   *
>>   * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
>>   */
>> -struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>> +static struct mux_control *mux_get(struct device *dev, const char *mux_name,
>> +				   unsigned int *enable_state)
> 
> s/enable_state/state/ (goes for all of the patch).
> 
>>  {
>>  	struct device_node *np = dev->of_node;
>>  	struct of_phandle_args args;
>> @@ -481,8 +545,7 @@ struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>>  	if (!mux_chip)
>>  		return ERR_PTR(-EPROBE_DEFER);
>>  
>> -	if (args.args_count > 1 ||
> 
> It is inconsistent to allow more than 2 args, but then only allow
> digging out the state from the 2nd arg if the count is exactly 2.
> 
>> -	    (!args.args_count && (mux_chip->controllers > 1))) {
>> +	if (!args.args_count && mux_chip->controllers > 1) {
>>  		dev_err(dev, "%pOF: wrong #mux-control-cells for %pOF\n",
>>  			np, args.np);
>>  		put_device(&mux_chip->dev);
>> @@ -500,8 +563,25 @@ struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>>  		return ERR_PTR(-EINVAL);
>>  	}
>>  
>> +	if (args.args_count == 2)
>> +		*enable_state = args.args[1];
>> +
> 
> With the suggested binding in my comment for patch 1/4, you'd need to do
> either
> 
> 	ret = of_parse_phandle_with_args(np,
> 					 "mux-controls", "#mux-control-cells",
> 					 index, &args);
> 
> or
> 
> 	ret = of_parse_phandle_with_args(np,
> 					 "mux-states", "#mux-state-cells",
> 					 index, &args);
> 
> depending on if the mux_get helper gets a NULL (enable_)state pointer or a "real"
> address, and then...
> 


Sorry, while trying to implement the above method, I came across one
more question. So, in a given consumer DT node we will be either having
only mux-states or mux-controls right? How would we take care of the
condition when we would want to set the state of a given line in the
controller. Especially when a single mux chip is used by multiple
consumers each using a different line. Wouldn't we require both
mux-controls and mux-states in that case? So, shouldn't the
implementation be such that we need to first read mux-controls and then
based whether the enable_state is NULL, we read mux-states?

Just to add more clarity, if we go about this method then we would have
both mux-controls and mux-states in the consumer DT node when we want to
specify the state.

Thanks,
Aswath

>>  	return &mux_chip->mux[controller];
>>  }
>> +
>> +/**
>> + * mux_control_get() - Get the mux-control for a device.
>> + * @dev: The device that needs a mux-control.
>> + * @mux_name: The name identifying the mux-control.
>> + *
>> + * Return: A pointer to the mux-control, or an ERR_PTR with a negative errno.
>> + */
>> +struct mux_control *mux_control_get(struct device *dev, const char *mux_name)
>> +{

[...]