usb: pd: Exposing the Peak Current value of Fixed Supplies to user space

Exposing the value of the field as is.

The Peak Current value has to be interpreted as described
in Table 6-10 (Fixed Power Source Peak Current Capability)
of the USB Power Delivery Specification, but that
interpretation will be done in user space, not in kernel.

Suggested-by: Douglas Gilbert <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Heikki Krogerus <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-class-usb_power_delivery

···
 Description:
 		The voltage the supply supports in millivolts.
 
+What:		/sys/class/usb_power_delivery/.../source-capabilities/<position>:fixed_supply/peak_current
+Date:		October 2023
+Contact:	Heikki Krogerus <[e-mail]>
+Description:
+		This file shows the value of the Fixed Power Source Peak Current
+		Capability field.
+
 What:		/sys/class/usb_power_delivery/.../source-capabilities/<position>:fixed_supply/maximum_current
 Date:		May 2022
 Contact:	Heikki Krogerus <[e-mail]>

drivers/usb/typec/pd.c

···
 }
 static DEVICE_ATTR_RO(unchunked_extended_messages_supported);
 
-/*
- * REVISIT: Peak Current requires access also to the RDO.
 static ssize_t
 peak_current_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
-	...
+	return sysfs_emit(buf, "%u\n", (to_pdo(dev)->pdo >> PDO_FIXED_PEAK_CURR_SHIFT) & 3);
 }
-*/
+static DEVICE_ATTR_RO(peak_current);
 
 static ssize_t
 fast_role_swap_current_show(struct device *dev, struct device_attribute *attr, char *buf)
···
 	&dev_attr_usb_communication_capable.attr,
 	&dev_attr_dual_role_data.attr,
 	&dev_attr_unchunked_extended_messages_supported.attr,
-	/*&dev_attr_peak_current.attr,*/
+	&dev_attr_peak_current.attr,
 	&dev_attr_voltage.attr,
 	&maximum_current_attr.attr,
 	NULL
···
 static umode_t fixed_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n)
 {
 	if (to_pdo(kobj_to_dev(kobj))->object_position &&
-	    /*attr != &dev_attr_peak_current.attr &&*/
+	    attr != &dev_attr_peak_current.attr &&
 	    attr != &dev_attr_voltage.attr &&
 	    attr != &maximum_current_attr.attr &&
 	    attr != &operational_current_attr.attr)

include/linux/usb/pd.h

···
 #define PDO_FIXED_UNCHUNK_EXT		BIT(24) /* Unchunked Extended Message supported (Source) */
 #define PDO_FIXED_FRS_CURR_MASK		(BIT(24) | BIT(23)) /* FR_Swap Current (Sink) */
 #define PDO_FIXED_FRS_CURR_SHIFT	23
+#define PDO_FIXED_PEAK_CURR_SHIFT	20
 #define PDO_FIXED_VOLT_SHIFT		10	/* 50mV units */
 #define PDO_FIXED_CURR_SHIFT		0	/* 10mA units */