linux-kernel - Re: [PATCH RFC v2 4/4] phy: phy-can-transceiver: Add support for setting mux

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Date:   Mon, 22 Nov 2021 18:50:00 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
CC:     Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Peter Rosin <peda@...ntia.se>,
        Rob Herring <robh+dt@...nel.org>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        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 v2 4/4] phy: phy-can-transceiver: Add support for
 setting mux

Hi Marc,

On 22/11/21 6:42 pm, Marc Kleine-Budde wrote:
> On 22.11.2021 18:26:24, Aswath Govindraju wrote:
>> On some boards, for routing CAN signals from controller to transceiver,
>> muxes might need to be set. Therefore, add support for setting the mux by
>> reading the mux-controls property from the device tree node.
>>
>> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
>> ---
>>  drivers/phy/phy-can-transceiver.c | 26 ++++++++++++++++++++++++++
>>  1 file changed, 26 insertions(+)
>>
>> diff --git a/drivers/phy/phy-can-transceiver.c b/drivers/phy/phy-can-transceiver.c
>> index 6f3fe37dee0e..15056b9d68ba 100644
>> --- a/drivers/phy/phy-can-transceiver.c
>> +++ b/drivers/phy/phy-can-transceiver.c
>> @@ -10,6 +10,7 @@
>>  #include<linux/module.h>
>>  #include<linux/gpio.h>
>>  #include<linux/gpio/consumer.h>
>> +#include <linux/mux/consumer.h>
>>  
>>  struct can_transceiver_data {
>>  	u32 flags;
>> @@ -21,13 +22,23 @@ struct can_transceiver_phy {
>>  	struct phy *generic_phy;
>>  	struct gpio_desc *standby_gpio;
>>  	struct gpio_desc *enable_gpio;
>> +	struct mux_control *mux_ctrl;
>>  };
>>  
>>  /* Power on function */
>>  static int can_transceiver_phy_power_on(struct phy *phy)
>>  {
>> +	int ret;
>>  	struct can_transceiver_phy *can_transceiver_phy = phy_get_drvdata(phy);
>>  
>> +	if (can_transceiver_phy->mux_ctrl) {
>> +		ret = mux_control_select(can_transceiver_phy->mux_ctrl,
>> +					 mux_control_enable_state(can_transceiver_phy->mux_ctrl));
>> +		if (ret) {
>> +			dev_err(&phy->dev, "Failed to select CAN mux: %d\n", ret);
>> +			return ret;
>> +		}
>> +	}
>>  	if (can_transceiver_phy->standby_gpio)
>>  		gpiod_set_value_cansleep(can_transceiver_phy->standby_gpio, 0);
>>  	if (can_transceiver_phy->enable_gpio)
>> @@ -45,6 +56,8 @@ static int can_transceiver_phy_power_off(struct phy *phy)
>>  		gpiod_set_value_cansleep(can_transceiver_phy->standby_gpio, 1);
>>  	if (can_transceiver_phy->enable_gpio)
>>  		gpiod_set_value_cansleep(can_transceiver_phy->enable_gpio, 0);
>> +	if (can_transceiver_phy->mux_ctrl)
>> +		mux_control_deselect(can_transceiver_phy->mux_ctrl);
>>  
>>  	return 0;
>>  }
>> @@ -95,6 +108,19 @@ static int can_transceiver_phy_probe(struct platform_device *pdev)
>>  	match = of_match_node(can_transceiver_phy_ids, pdev->dev.of_node);
>>  	drvdata = match->data;
>>  
>> +	if (of_property_read_bool(dev->of_node, "mux-controls")) {
>> +		struct mux_control *control;
>> +		int ret;
>> +
>> +		control = devm_mux_control_get(dev, NULL);
>> +		if (IS_ERR(control)) {
>> +			ret = PTR_ERR(control);
>> +			dev_err_probe(&pdev->dev, ret, "failed to get mux\n");
>> +			return PTR_ERR(control);
>> +		}
>> +		can_transceiver_phy->mux_ctrl = control;
>> +	}
> 
> What about adding a devm_mux_control_get_optional(), which doesn't
> return a -ENODEV but a NULL pointer if the device doesn't exist?
> 

I tried adding it in the following manner,

+/**
+ * devm_mux_control_optional_get() - Optionally get the mux-control for a
+ *                                  device, with resource management.
+ * @dev: The device that needs a mux-control.
+ * @mux_name: The name identifying the mux-control.
+ *
+ * This differs from devm_mux_control_get in that if the mux does not
+ * exist, it is not considered an error and -ENODEV will not be
+ * returned. Instead the NULL is returned.
+ *
+ * Return: Pointer to the mux-control, or an ERR_PTR with a negative errno.
+ */
+struct mux_control *devm_mux_control_optional_get(struct device *dev,
+                                                 const char *mux_name)
+{
+       struct mux_control *mux_ctrl;
+
+       mux_ctrl = devm_mux_control_get(dev, mux_name);
+       if (PTR_ERR(mux_ctrl) == -ENOENT)
+                mux_ctrl = NULL;
+
+       return mux_ctrl;
+}
+EXPORT_SYMBOL_GPL(devm_mux_control_optional_get);
+

However the issue is that there is a print in mux_control_get()
 dev_err(dev, "%pOF: failed to get mux-control %s(%i)\n",

which is getting printed, whenever mux-controls property is not found.
Therefore, I was not sure about how to go about this issue and did not
implement it.

Thanks,
Aswath

> Marc
>