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

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Date:   Tue, 15 Sep 2020 23:14:18 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Alexander Dahl <ada@...rsis.com>
Cc:     Alexander Dahl <post@...pocky.de>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, Pavel Machek <pavel@....cz>,
        Dan Murphy <dmurphy@...com>, Rob Herring <robh+dt@...nel.org>,
        linux-kernel@...r.kernel.org,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH v4 1/3] leds: Require valid fwnode pointer for composing
 name

Hi Alexander,

On 9/15/20 11:14 AM, Alexander Dahl wrote:
> 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@....cz>
>>> Signed-off-by: Alexander Dahl <post@...pocky.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?

In fact it looks like that patch was pointless, since it precluded the
use of struct led_pwm_platform_data anywhere besides the leds-pwm
driver.

> 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?

git grep led_pwm_platform_data in fact shows only references in
leds-pwm.c, so yes, I think the platform support seems to be redundant.

-- 
Best regards,
Jacek Anaszewski