Re: [PATCH 2/6] wl1251: Use request_firmware_prefer_user() for loading NVS calibration data

From: Kalle Valo <kvalo@codeaurora.org>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: Arend Van Spriel <arend.vanspriel@broadcom.com>,
	Ming Lei <ming.lei@canonical.com>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	David Gnedt <david.gnedt@davizone.at>,
	Michal Kazior <michal.kazior@tieto.com>,
	Daniel Wagner <wagi@monom.org>, Tony Lindgren <tony@atomide.com>,
	Sebastian Reichel <sre@kernel.org>, Pavel Machek <pavel@ucw.cz>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
	Aaro Koskinen <aaro.koskinen@iki.fi>,
	Grazvydas Ignotas <notasas@gmail.com>,
	linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH 2/6] wl1251: Use request_firmware_prefer_user() for loading NVS calibration data
Date: Fri, 27 Jan 2017 14:26:22 +0200	[thread overview]
Message-ID: <8737g47kpd.fsf@kamboji.qca.qualcomm.com> (raw)
In-Reply-To: <20170127115706.GH24223@pali> ("Pali \=\?utf-8\?Q\?Roh\=C3\=A1r\=22'\?\= \=\?utf-8\?Q\?s\?\= message of "Fri, 27 Jan 2017 12:57:06 +0100")

Pali Rohár <pali.rohar@gmail.com> writes:

> On Friday 27 January 2017 13:49:03 Kalle Valo wrote:
>> Pali Rohár <pali.rohar@gmail.com> writes:
>> 
>> >> So
>> >> for those other platforms there will be a delay waiting for user-mode
>> >> helper to fail, before trying to get nvs file from /lib/firmware.
>> >
>> > Yes, there will be. But there is no easy way to fix this problem that
>> > kernel is trying to use default/example NVS data...
>> 
>> Kernel is doing correctly and requesting NVS data as expected, the
>> problem here is that linux-firmware claims that the example NVS data is
>> real calibration data (which it is not). Distros should not use that,
>> only developers for testing purposes. We should not courage users using
>> example calibration data.
>> 
>> The simple fix is to rename the NVS file in linux-firmware to something
>> like wl1251-nvs.bin.example, no need to workaround this in kernel. If
>> you send a patch to linux-firmware I'm happy to ack that.
>
> I agree with rename and fact that default/example data should not be
> used.
>
> But...
>
> 1) Kernel should not read device/model specific data from VFS where
> are stored not-device-specific files preinstalled by linux
> distributions.
>
> And linux distributions are already putting files into VFS and kernel
> cannot enforce userspace to not do that (as they are already doing it).

I'm having problems to understand what you are saying here.

> 2) It was already tested that example NVS data can be used for N900 e.g.
> for SSH connection. If real correct data are not available it is better
> to use at least those example (and probably log warning message) so user
> can connect via SSH and start investigating where is problem.

I disagree. Allowing default calibration data to be used can be
unnoticed by user and left her wondering why wifi works so badly.

> 3) If we do rename *now* we will totally break wifi support on Nokia
> N900.

Then the distro should fix that when updating the linux-firmware
packages. Can you provide details about the setup, what distro etc?

-- 
Kalle Valo