Re: [PATCH 5/5] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

[Jacek Anaszewski <jacek.anaszewski@gmail.com>]

On 12/19/2016 09:08 PM, Pavel Machek wrote:
> Hi!
> 
>> On 12/17/2016 01:14 AM, Luis R. Rodriguez wrote:
>>> Milo if sysfs is used can't the old userspace be mapped to use the new
>>> sysfs interface through a wrapper of some sort ? What exactly would be
>>> needed to ensure old userspace will not break?
>>
>> LP5521 and LP5523 have two ways to load hex code from the userspace - the
>> sysfs and firmware I/F. So user program supports both interfaces. Even if
>> the firmware I/F is not available, user can still run LED effect through the
>> sysfs.
>>
>> However, LP5562 and LP8501 support only single way which is the firmware
>> I/F. So user-space program for LP5562/8501 should be modified if lp55xx
>> removes the interface. My idea is
> 
> Actually... it would be good to have some reasonable interface for RGB
> LEDs. This way, we need separate "firmware" for each LED
> controller. It would be good to have common format for LED effects.

We still haven't tried trigger approach discussed over half a year ago.
If we used firmware approach we would still have to overcome the problem
of defining the LED class drivers affected by the firmware program.

>>   Phase 1)
>>   - create sysfs in LP5562 and LP8501
>>   - use new sysfs inside the firmware I/F loading callback
>>   - mark the firmware callback as a deprecated interface
> 
> Phase 1a)
> 
> stick WARN_ON() in the firmware callback.
> 
>>   Phase 2)
>>   - remove the firmware I/F after all user program fixes the interface
>>     (but the problem is how can we get to know when this is done?)
>>
>>> Why has no one cried
>>> after the v4.0 custom fallback mechanism breaking ?
>>
>> Well, I don't know the reason exactly but my guess is they maybe still using
>> old kernel.
>>
>>> How wide spread is this custom userspace ?
>>
>> Device manufactures in Asia & North America requested lp55xx drivers, but I
>> don't know how many vendors uses the firmware I/F. Some vendors embeds the
>> binary code inside the driver instead of using user-program.
> 
> Nokia N900 uses lp55xx, and I have custom scripts interfacing sysfs.
> 
> Maemo uses the LEDs, too, but maemo is not open source.
> 
> So no, I don't think there's anything important that could be broken.

We can't guarantee that. Is there any problem in just using the
currently introduced DECLARE_FW_CUSTOM_FALLBACK() in
drivers/leds/leds-lp55xx-common.c?

-- 
Best regards,
Jacek Anaszewski