linux-kernel - Re: [PATCH v1] usb: typec: altmodes/displayport: Add hpd sysfs attribute

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Date:   Tue, 13 Dec 2022 11:21:30 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Badhri Jagan Sridharan <badhri@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        RD Babiera <rdbabiera@...gle.com>
Subject: Re: [PATCH v1] usb: typec: altmodes/displayport: Add hpd sysfs
 attribute

On Sun, Dec 11, 2022 at 11:37:55AM -0800, Badhri Jagan Sridharan wrote:
> 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@...gle.com>

Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  .../ABI/testing/sysfs-driver-typec-displayport    | 15 +++++++++++++++
>  drivers/usb/typec/altmodes/displayport.c          | 10 ++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-driver-typec-displayport b/Documentation/ABI/testing/sysfs-driver-typec-displayport
> index 231471ad0d4b..256c87c5219a 100644
> --- a/Documentation/ABI/testing/sysfs-driver-typec-displayport
> +++ b/Documentation/ABI/testing/sysfs-driver-typec-displayport
> @@ -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@...gle.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.
> diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index de66a2949e33..06fb4732f8cd 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -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
>  };
>  
> 
> base-commit: 81c25247a2a03a0f97e4805d7aff7541ccff6baa
> -- 
> 2.39.0.rc1.256.g54fd8350bd-goog

thanks,

-- 
heikki