linux-kernel - Re: [PATCH v2] usb: typec: Expose Product Type VDOs via sysfs

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Date:   Thu, 22 Oct 2020 08:57:19 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Benson Leung <bleung@...omium.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Subject: Re: [PATCH v2] usb: typec: Expose Product Type VDOs via sysfs

On Wed, Oct 21, 2020 at 11:15:54PM -0700, Prashant Malani wrote:
> A PD-capable device can return up to 3 Product Type VDOs as part of its
> DiscoverIdentity Response (USB PD Spec, Rev 3.0, Version 2.0, Section
> 6.4.4.3.1). Add a sysfs attribute to expose these to userspace.
> 
> Cc: Benson Leung <bleung@...omium.org>
> Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Signed-off-by: Prashant Malani <pmalani@...omium.org>
> ---
> 
> NOTE: I didn't include Benson's Reviewed-by from v1, since this version
> introduced the sysfs_notify() call.
> 
> Changes in v2:
> - Added sysfs_notify() call for the attribute.
> - Added description for the attribute in
>   Documentation/ABI/testing/sysfs-class-typec.
> 
>  Documentation/ABI/testing/sysfs-class-typec | 17 +++++++++++++++++
>  drivers/usb/typec/class.c                   | 11 +++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-typec b/Documentation/ABI/testing/sysfs-class-typec
> index b834671522d6..16440a236b66 100644
> --- a/Documentation/ABI/testing/sysfs-class-typec
> +++ b/Documentation/ABI/testing/sysfs-class-typec
> @@ -170,6 +170,14 @@ Description:
>  		will show 0 until Discover Identity command result becomes
>  		available. The value can be polled.
>  
> +What:		/sys/class/typec/<port>-partner/identity/product_type_vdo
> +Date:		October 2020
> +Contact:	Prashant Malani <pmalani@...omium.org>
> +Description:
> +		Product Type VDOs part of Discover Identity command result. 3 values
> +		are displayed (for the 3 possible Product Type VDOs), one per line.

sysfs is "one value per file", not "one value per line".  This is not
ok.

> +		The values will show 0s until Discover Identity command result becomes
> +		available. The values can be polled.

It can be polled?  Did you try that?  I don't see the logic for that in
your patch.


>  
>  USB Type-C cable devices (eg. /sys/class/typec/port0-cable/)
>  
> @@ -230,6 +238,15 @@ Description:
>  		will show 0 until Discover Identity command result becomes
>  		available. The value can be polled.
>  
> +What:		/sys/class/typec/<port>-cable/identity/product_type_vdo
> +Date:		October 2020
> +Contact:	Prashant Malani <pmalani@...omium.org>
> +Description:
> +		Product Type VDOs part of Discover Identity command result. 3 values
> +		are displayed (for the 3 possible Product Type VDOs), one per line.
> +		The values will show 0s until Discover Identity command result becomes
> +		available. The values can be polled.

Why are you describing the same value in two different locations?

> +
>  
>  USB Type-C port alternate mode devices.
>  
> diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
> index 35eec707cb51..37fa4501e75f 100644
> --- a/drivers/usb/typec/class.c
> +++ b/drivers/usb/typec/class.c
> @@ -122,10 +122,20 @@ static ssize_t product_show(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RO(product);
>  
> +static ssize_t product_type_vdo_show(struct device *dev, struct device_attribute *attr,
> +				     char *buf)
> +{
> +	struct usb_pd_identity *id = get_pd_identity(dev);
> +
> +	return sprintf(buf, "0x%08x\n0x%08x\n0x%08x\n", id->vdo[0], id->vdo[1], id->vdo[2]);

Note, for future sysfs stuff, always use sysfs_emit().

But again, this is not allowed as you have multiple values per a single
file.

thanks,

greg k-h