linux-kernel - Re: [PATCH 5/5] firmware: add DECLARE_FW_CUSTOM

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Date:   Sun, 18 Dec 2016 12:50:43 +0900
From:   Milo Kim <woogyom.kim@...il.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, gregkh@...uxfoundation.org,
        ming.lei@...onical.com, daniel.wagner@...-carit.de, teg@...m.no,
        mchehab@....samsung.com, zajec5@...il.com,
        linux-kernel@...r.kernel.org, markivx@...eaurora.org,
        stephen.boyd@...aro.org, broonie@...nel.org,
        zohar@...ux.vnet.ibm.com, tiwai@...e.de, johannes@...solutions.net,
        chunkeey@...glemail.com, hauke@...ke-m.de,
        jwboyer@...oraproject.org, dmitry.torokhov@...il.com,
        dwmw2@...radead.org, jslaby@...e.com,
        torvalds@...ux-foundation.org, luto@...capital.net,
        fengguang.wu@...el.com, rpurdie@...ys.net,
        j.anaszewski@...sung.com, Abhay_Salunke@...l.com,
        Julia.Lawall@...6.fr, Gilles.Muller@...6.fr, nicolas.palix@...g.fr,
        dhowells@...hat.com, bjorn.andersson@...aro.org,
        arend.vanspriel@...adcom.com, kvalo@...eaurora.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH 5/5] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

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