linux-kernel - Re: [RFC PATCH 3/3] usb: typec: Expose Product Type VDOs via sysfs

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Date:   Thu, 19 Nov 2020 14:11:07 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Prashant Malani <pmalani@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] usb: typec: Expose Product Type VDOs via sysfs

On Wed, Nov 18, 2020 at 04:56:57PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 18, 2020 at 06:00:59PM +0300, Heikki Krogerus wrote:
> > From: Prashant Malani <pmalani@...omium.org>
> > 
> > Interim. ABI doc missing.
> > 
> > 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 sysfs attribute to expose these to userspace.
> > 
> > Signed-off-by: Prashant Malani <pmalani@...omium.org>
> > [ heikki: Only one instead of three attribute files ]
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>'
> > ---
> >  drivers/usb/typec/class.c | 41 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> > 
> > diff --git a/drivers/usb/typec/class.c b/drivers/usb/typec/class.c
> > index 303f054181ff7..5e135678f5952 100644
> > --- a/drivers/usb/typec/class.c
> > +++ b/drivers/usb/typec/class.c
> > @@ -165,15 +165,55 @@ 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);
> > +	size_t len = 0;
> > +	int i;
> > +
> > +	for (i = 0; i < 3; i++) {
> > +		if (!id->vdo[i])
> > +			break;
> > +		len += sysfs_emit(buf, "%08x ", id->vdo[i]);
> > +	}
> > +
> > +	buf[len - 1] = '\n';
> > +
> > +	return len;
> > +}
> 
> I don't understand what you are trying to print out here, documentation
> would be helpful :)
> 
> > +static struct device_attribute dev_attr_product_type_vdo = {
> > +	.attr = {
> > +		.name = "product_type",
> > +		.mode = 0444,
> > +	},
> > +	.show = product_type_vdo_show,
> > +};
> 
> DEVICE_ATTR_RO(product_type_vdo)?
> 
> Why are you calling it "product_type" and not with the "vdo"?
> 
> And you have to name it this, there's always __ATTR_RO(), never put a
> mode in "raw" numbers for a sysfs file if at all possible.

Sorry Greg. This is still work-in-progress.

I didn't use the _vdo ending in the file name because the other files
exposing the other parts (VDOs) of the response to the discover
identity don't have it either.


thanks,

-- 
heikki