Re: [RFC] drm/msm/dp: Allow attaching a drm_panel

[Bjorn Andersson <andersson@kernel.org>]

On Mon, May 22, 2023 at 03:51:01PM -0500, Bjorn Andersson wrote:
> On Fri, Oct 08, 2021 at 03:38:21PM +0300, Heikki Krogerus wrote:
> > Hi,
> > 
> > On Thu, Oct 07, 2021 at 09:15:12AM -0700, Bjorn Andersson wrote:
> > > The one thing that I still don't understand though is, if the typec_mux
> > > is used by the typec controller to inform _the_ mux about the function
> > > to be used, what's up with the complexity in typec_mux_match()? This is
> > > what lead me to believe that typec_mux was enabling/disabling individual
> > > altmodes, rather just flipping the physical switch at the bottom.
> > 
> > Ah, typec_mux_match() is a mess. I'm sorry about that. I think most of
> > the code in that function is not used by anybody. If I remember
> > correctly, all that complexity is attempting to solve some
> > hypothetical corner case(s). Probable a case where we have multiple
> > muxes per port to deal with.
> > 
> > I think it would probable be best to clean the function to the bare
> > minimum by keeping only the parts that are actually used today
> > (attached).
> > 
> 
> Sorry for not replying to this in a timely manner Heikki. I've been
> ignoring this issue for a long time now, just adding "svid" to our dts
> files. But, this obviously shows up in DT validation - and I'd prefer
> not defining these properties as valid.
> 
> The attached patch works as expected.
> 

Sorry, I must have failed at applying the patch - it doesn't work...

> Could you please spin this as a proper patch, so we can get it merged?
> 
> Regards,
> Bjorn
> 
> > thanks,
> > 
> > -- 
> > heikki
> 
> > diff --git a/drivers/usb/typec/mux.c b/drivers/usb/typec/mux.c
> > index c8340de0ed495..44f168c9bd9bf 100644
> > --- a/drivers/usb/typec/mux.c
> > +++ b/drivers/usb/typec/mux.c
> > @@ -193,56 +193,15 @@ static int mux_fwnode_match(struct device *dev, const void *fwnode)
> >  static void *typec_mux_match(struct fwnode_handle *fwnode, const char *id,
> >  			     void *data)
> >  {
> > -	const struct typec_altmode_desc *desc = data;
> >  	struct device *dev;
> > -	bool match;
> > -	int nval;
> > -	u16 *val;
> > -	int ret;
> > -	int i;
> >  
> >  	/*
> > -	 * Check has the identifier already been "consumed". If it
> > -	 * has, no need to do any extra connection identification.
> > +	 * The connection identifier will be needed with device graph (OF graph).
> > +	 * Device graph is not supported by this code yet, so bailing out.
> >  	 */
> > -	match = !id;
> > -	if (match)
> > -		goto find_mux;
> > -
> > -	/* Accessory Mode muxes */
> > -	if (!desc) {
> > -		match = fwnode_property_present(fwnode, "accessory");
> > -		if (match)
> > -			goto find_mux;
> > -		return NULL;
> > -	}
> > -
> > -	/* Alternate Mode muxes */
> > -	nval = fwnode_property_count_u16(fwnode, "svid");
> > -	if (nval <= 0)
> > -		return NULL;
> > -
> > -	val = kcalloc(nval, sizeof(*val), GFP_KERNEL);
> > -	if (!val)
> > -		return ERR_PTR(-ENOMEM);
> > -
> > -	ret = fwnode_property_read_u16_array(fwnode, "svid", val, nval);
> > -	if (ret < 0) {
> > -		kfree(val);
> > -		return ERR_PTR(ret);
> > -	}
> > -
> > -	for (i = 0; i < nval; i++) {
> > -		match = val[i] == desc->svid;
> > -		if (match) {
> > -			kfree(val);
> > -			goto find_mux;
> > -		}
> > -	}
> > -	kfree(val);
> > -	return NULL;
> > +	if (id)

We pass id as "mode-switch", so this will never be NULL. But we also only
want to consider endpoints with "mode-switch", otherwise we'll fail if
any of the referred endpoints is not implementing a typec_mux...

So this needs the same snippet we find in typec_switch_match():

	/*
	 * Device graph (OF graph) does not give any means to identify the
	 * device type or the device class of the remote port parent that @fwnode
	 * represents, so in order to identify the type or the class of @fwnode
	 * an additional device property is needed. With typec switches the
	 * property is named "orientation-switch" (@id). The value of the device
	 * property is ignored.
	 */
	if (id && !fwnode_property_present(fwnode, id))
	        return NULL;

With that, this works as expected!

Regards,
Bjorn

> > +		return ERR_PTR(-ENOTSUPP);
> >  
> > -find_mux:
> >  	dev = class_find_device(&typec_mux_class, NULL, fwnode,
> >  				mux_fwnode_match);
> >  
>