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

[Milo Kim]

Hi Luis,

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

  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 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.

I understood it's a kind of troublesome work in terms of the 
maintenance. Sorry for that. I hope we have a consensus to resolve it.
Thanks!

Best regards,
Milo