netdev - Re: [PATCH] leds: trigger: netdev: skip setting baseline state in activate if hw-controlled

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Date: Wed, 6 Dec 2023 19:32:54 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
 Christian Marangi <ansuelsmth@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] leds: trigger: netdev: skip setting baseline state in
 activate if hw-controlled

On 06.12.2023 18:45, Andrew Lunn wrote:
>>>> I actually think we need to define some best practices, ordered on
>>>> what the hardware can do.
>>>>
>>>> 1) With software control, set_brightness should do what you expect,
>>>> not return an error.
>>>>
>>>> 2) Without full software control, but there is a mechanism to report a
>>>> problem, like constant blinking, or off, do that, and return
>>>> -EOPNOTSUPP.
>>>>
>>>> 3) Really dumb hardware like this, set_brightness should be a NULL
>>>> pointer. The core returns -EOPNOTSUPP.
>>>>
>>>> The core should return this -EOPNOTSUPP to user space, but it should
>>>> accept the configuration change. So the user can put it into an
>>>> invalid state, in order to get to a valid state with further
>>>> configuration.
>>>>
>>> Sounds good to me. Let me come up with a RFC patch.
>>>
>>>> I don't see an easy way to let the user know what the valid states
>>>> are. We currently have a 10bit state. I don't think we can put all the
>>>> valid ones in a /sysfs file, especially when QCA8K pretty much
>>>> supports everything.
>>>>
>>>> 	 Andrew
>>>
>>> Heiner
>>
>> Patch is so simple that I send it this way. What do you think?
> 
> That is simpler than i expected.
> 
> But i think we need to document our expectations. What do we expect an
> LED driver to do when it cannot support software blinking. So please
> could you add a comment somewhere. Maybe extend the
> 
> /*
>  *Configurable sysfs attributes:
>  *
> 
> section?
> 
Yes, this is a good place IMO. I'll submit a patch including the functional
change and the extended comment.

> Thanks
> 	Andrew

Heiner