linux-kernel - Re: [RFC] drm/msm/dp: Allow attaching a drm

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Message-ID: <do5veo5axxbvmcddpqf7u5rfer6soxzy5selfnjv5sn6n57h47@q3hfznslndba>
Date:   Mon, 22 May 2023 15:51:01 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Prashant Malani <pmalani@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Kuogee Hsieh <khsieh@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Vara Reddy <varar@...eaurora.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Benson Leung <bleung@...omium.org>
Subject: Re: [RFC] drm/msm/dp: Allow attaching a drm_panel

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.

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