linux-kernel - Re: [PATCH v3 4/6] typec: mux: Allow multiple mux

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Message-ID: <YiV3UYuXgS0w0IWl@yoga>
Date:   Sun, 6 Mar 2022 21:09:05 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v3 4/6] typec: mux: Allow multiple mux_devs per mux

On Fri 04 Mar 07:54 CST 2022, Andy Shevchenko wrote:

> On Thu, Mar 03, 2022 at 02:33:49PM -0800, Bjorn Andersson wrote:
> > In the Qualcomm platforms the USB/DP PHY handles muxing and orientation
> > switching of the SuperSpeed lines, but the SBU lines needs to be
> > connected and switched by external (to the SoC) hardware.
> > 
> > It's therefor necessary to be able to have the TypeC controller operate
> > multiple TypeC muxes and switches. Use the newly introduced indirection
> > object to handle this, to avoid having to taint the TypeC controllers
> > with knowledge about the downstream hardware configuration.
> > 
> > The max number of devs per indirection is set to 3, which account for
> > being able to mux/switch the USB HS, SS and SBU lines, as per defined
> > defined in the usb-c-connector binding. This number could be grown if
> > need arrises at a later point in time.
> 
> ...
> 
> > +	for (i = 0; i < count; i++) {
> > +		if (IS_ERR(sw_devs[i])) {
> > +			err = PTR_ERR(sw_devs[i]);
> > +			goto put_sw_devs;
> > +		}
> > +	}
> >  
> > -	sw->sw_dev = sw_dev;
> > +	for (i = 0; i < count; i++) {
> > +		WARN_ON(!try_module_get(sw_devs[i]->dev.parent->driver->owner));
> > +		sw->sw_devs[i] = sw_devs[i];
> > +	}
> > +
> > +	sw->num_sw_devs = count;
> >  
> >  	return sw;
> > +
> > +put_sw_devs:
> > +	for (i = 0; i < count; i++) {
> 
> Shouldn't it be
> 
> 	while (i--)
> 
> ?

fwnode_connection_find_matches() "returned" count number of sw_devs, we
need to put_device() them all. So that form could have been

	while (count--)

but as it's not the typical "unrolling" I think the untypical form is
more useful.

> 
> > +		if (!IS_ERR(sw_devs[i]))
> 
> We may get rid of this check if we guarantee that the device is NULL.
> 

In the event that the USB Type-C controller probes before some of the
muxes, this array might contain one or more entries of EPROBE_DEFER.

So we need to either put this conditional here, or we need to loop
through all entries to turn IS_ERR() into NULL, for the sake of not
having it here.

So to me this looks cleaner...

Regards,
Bjorn

> > +			put_device(&sw_devs[i]->dev);
> > +	}
> > +
> > +	kfree(sw);
> > +
> > +	return ERR_PTR(err);
> >  }
> 
> ...
> 
> > +	for (i = 0; i < count; i++) {
> > +		if (IS_ERR(mux_devs[i])) {
> > +			err = PTR_ERR(mux_devs[i]);
> > +			goto put_mux_devs;
> > +		}
> 
> Ditto.
> 
> > +	}
> 
> ...
> 
> > +put_mux_devs:
> > +	for (i = 0; i < count; i++) {
> > +		if (!IS_ERR(mux_devs[i]))
> > +			put_device(&mux_devs[i]->dev);
> > +	}
> 
> Ditto.
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>