Re: [PATCH v4 1/3] leds: Require valid fwnode pointer for composing name

From: Alexander Dahl <ada@thorsis.com>
To: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Alexander Dahl <post@lespocky.de>,
	linux-leds@vger.kernel.org, devicetree@vger.kernel.org,
	Pavel Machek <pavel@ucw.cz>, Dan Murphy <dmurphy@ti.com>,
	Rob Herring <robh+dt@kernel.org>,
	linux-kernel@vger.kernel.org,
	Peter Ujfalusi <peter.ujfalusi@ti.com>
Subject: Re: [PATCH v4 1/3] leds: Require valid fwnode pointer for composing name
Date: Tue, 15 Sep 2020 11:14:49 +0200	[thread overview]
Message-ID: <2642665.8NmDdnWKvZ@ada> (raw)
In-Reply-To: <6652b897-5044-713b-6f06-83d07be0dba7@gmail.com>

Hello Jacek,

thanks for your feedback. See below.

Am Freitag, 11. September 2020, 23:26:43 CEST schrieb Jacek Anaszewski:
> On 9/11/20 5:40 PM, Alexander Dahl wrote:
> > The function 'led_compose_name()' is called in
> > 'led_classdev_register_ext(()' only and in its implementation it always
> > parses the fwnode passed with the init_data struct.  If there's no
> > fwnode, EINVAL is returned and 'led_classdev_register_ext()' returns
> > early.
> > 
> > If this is detected early the same fallback mechanism can be used , as
> > if init_data itself is NULL.  This will allow drivers to pass fully
> > populated 'init_data' or sparse initialized 'init_data' with a NULL
> > fwnode in a more elegant way with only one function call.
> > 
> > Fixes: bb4e9af0348d ("leds: core: Add support for composing LED class
> > device names") Suggested-by: Pavel Machek <pavel@ucw.cz>
> > Signed-off-by: Alexander Dahl <post@lespocky.de>
> > ---
> > 
> > Notes:
> >      v4:
> >        * added this patch to series (Suggested-by: Pavel Machek)
> >   
> >   drivers/leds/led-class.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> > index cc3929f858b6..3da50c7ecfe7 100644
> > --- a/drivers/leds/led-class.c
> > +++ b/drivers/leds/led-class.c
> > @@ -346,7 +346,7 @@ int led_classdev_register_ext(struct device *parent,
> > 
> >   	const char *proposed_name = composed_name;
> >   	int ret;
> > 
> > -	if (init_data) {
> > +	if (init_data && init_data->fwnode) {
> 
> This does not cover the case when we don't have fwnode but we
> have init_data->default_label that led_compose_name() can make use of.
> 
> >   		if (init_data->devname_mandatory && !init_data->devicename) {
> >   		
> >   			dev_err(parent, "Mandatory device name is missing");
> >   			return -EINVAL;

You're right, I missed that part in that if/else if construct in 
led_compose_name() … I looked at the code for some more time now and could not 
come up with an elegant change to the led-core or led-class. :-/

However I also had another look at leds-pwm and for me it seems that it is 
used by fwnode (DT, ACPI, ??) based devices only.  I could not find a single 
user of leds-pwm as a platform driver, which is probably why 141f15c66d94 
("leds: pwm: remove header") was possible?

I had a look at the history of the leds-pwm driver and when introduced in 2009 
platform based board files where a thing, no dt, of, or fwnode yet, at least 
for arm, right?  Device tree support for leds-pwm was added in 2012 by Peter 
Ujfalusi.

So if those code paths in leds-pwm are not used anymore, what about dropping 
that platform support in leds-pwm driver?  That would mean we always have 
fwnode non-null and would not require a change in led-class at all?

Greets
Alex