linux-kernel - Re: [PATCH] si2157: Add support for Logilink VG0022A.

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Message-ID: <23d9856c-cc12-7212-9126-90d80f67abfb@jpvw.nl>
Date:   Fri, 4 Oct 2019 13:50:43 +0200
From:   JP <jp@...w.nl>
To:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Gonsolo <gonsolo@...il.com>
Cc:     crope@....fi, Sean Young <sean@...s.org>,
        linux-media@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] si2157: Add support for Logilink VG0022A.



On 10/3/19 10:03 PM, Mauro Carvalho Chehab wrote:
> Em Thu, 3 Oct 2019 21:51:35 +0200
> Gonsolo <gonsolo@...il.com> escreveu:
>
>>> 1) The firmware file is likely at the Windows driver for this device
>>> (probably using a different format). It should be possible to get
>>> it from there.
>> If you tell me how I'm willing to do this. :)
> I don't know. I was not the one that extracted the firmware. I guess
> Antti did it.
>
> I suspect that there are some comments about that in the past at the
> ML. seek at lore.kernel.org.
>
>>> 2) Another possibility would be to add a way to tell the si2168 driver
>>> to not try to load a firmware, using the original one. That would
>>> require adding a field at si2168_config to allow signalizing to it
>>> that it should not try to load a firmware file, and add a quirk at
>>> the af9035 that would set such flag for Logilink VG0022A.
>> I don't get this. Which firmware, si2168 or si2157?
> The one that it is causing the problem. If I understood well, the
> culprit was the si2168 firmware.
>
>> I'm still for option 3: If there is a bogus chip revision number it's
>> likely the VG0022A and we can safely set fw to NULL, in which case
>> everything works.
>> All already working devices will continue to work as before.
>> With a low probability there are other devices that will return 0xffff
>> but a) they didn't work until now and b) they receive a clear message
>> that they return bogus numbers and this works just for the VG0022A, in
>> which case this hardware can be tested.
>> At last, *my* VG0022A will work without a custom kernel which I'm a
>> big fan of. :))
>>
>> Are there any counterarguments except that it is not the cleanest
>> solution in the universe? ;)
> That's a really bad solution. Returning 0xff is what happens when
> things go wrong during I2C transfers. Several problems can cause it,
> including device misfunction. Every time someone comes with a patch
> trying to ignore it, things go sideways for other devices (existing
> or future ones).
>
> Ignoring errors is always a bad idea.
add module param say 'gonso_hack_vg0022a'
if true, act on error by setting a flag
if this flag is set don't load firmware

Jan Pieter.