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usb: typec: altmodes/displayport: Add hpd sysfs attribute 

Exporsing HotPlugDetect(HPD) helps userspace to infer HPD
state as defined by VESA DisplayPort Alt Mode on USB Type-C Standard.
This allows userspace to notify users for self help, for instance,
to hint user that the display port cable is probably detached (or)
the display port sink (viz., monitors ect.,) is un-powered.
Also helps to debug issues reported from field.

This change adds an additional attribute "hpd" to the existing
"displayport" attributes.

VESA DisplayPort Alt Mode on USB Type-C Standard defines how
HotPlugDetect(HPD) shall be supported on the USB-C connector
when operating in DisplayPort Alt Mode. This is a read only
node which reflects the current state of HPD.

Valid values:
 - 1 when HPD’s logical state is high (HPD_High)
 - 0 when HPD’s logical state is low (HPD_Low)

Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20221211193755.1392128-1-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Badhri Jagan Sridharan 2022-12-11 11:37:55 -08:00 committed by Greg Kroah-Hartman
parent 1b929c02af
commit 001b0c780e
2 changed files with 25 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
Documentation/ABI/testing/sysfs-driver-typec-displayport
View File

@ -47,3 +47,18 @@ Description:
USB SuperSpeed protocol. From user perspective pin assignments C
and E are equal, where all channels on the connector are used
for carrying DisplayPort protocol (allowing higher resolutions).
What: /sys/bus/typec/devices/.../displayport/hpd
Date: Dec 2022
Contact: Badhri Jagan Sridharan <badhri@google.com>
Description:
VESA DisplayPort Alt Mode on USB Type-C Standard defines how
HotPlugDetect(HPD) shall be supported on the USB-C connector when
operating in DisplayPort Alt Mode. This is a read only node which
reflects the current state of HPD.
Valid values:
- 1: when HPD’s logical state is high (HPD_High) as defined
by VESA DisplayPort Alt Mode on USB Type-C Standard.
- 0 when HPD’s logical state is low (HPD_Low) as defined by
VESA DisplayPort Alt Mode on USB Type-C Standard.

10
drivers/usb/typec/altmodes/displayport.c
View File

@ -146,6 +146,7 @@ static int dp_altmode_status_update(struct dp_altmode *dp)
if (dp->hpd != hpd) {
drm_connector_oob_hotplug_event(dp->connector_fwnode);
dp->hpd = hpd;
sysfs_notify(&dp->alt->dev.kobj, "displayport", "hpd");
}
}
@ -508,9 +509,18 @@ static ssize_t pin_assignment_show(struct device *dev,
}
static DEVICE_ATTR_RW(pin_assignment);
static ssize_t hpd_show(struct device *dev, struct device_attribute *attr, char *buf)
{
struct dp_altmode *dp = dev_get_drvdata(dev);
return sysfs_emit(buf, "%d\n", dp->hpd);
}
static DEVICE_ATTR_RO(hpd);
static struct attribute *dp_altmode_attrs[] = {
&dev_attr_configuration.attr,
&dev_attr_pin_assignment.attr,
&dev_attr_hpd.attr,
NULL
};