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

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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@xxxxxx>
Signed-off-by: Alexander Dahl <post@xxxxxxxxxxx>
---

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



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