linux-kernel - Re: [PATCH] ARM: exynos_defconfig: Enable WiFi-Ex as a module instead built-in

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Message-ID: <560B8DA3.6060507@osg.samsung.com>
Date:	Wed, 30 Sep 2015 09:22:11 +0200
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	linux-kernel@...r.kernel.org
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Kukjin Kim <kgene@...nel.org>,
	Thierry Reding <treding@...dia.com>,
	Anand Moon <linux.amoon@...il.com>,
	Russell King <linux@....linux.org.uk>,
	linux-samsung-soc@...r.kernel.org,
	Andreas Faerber <afaerber@...e.de>,
	Lukasz Majewski <l.majewski@...sung.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: exynos_defconfig: Enable WiFi-Ex as a module instead
 built-in

Hello Krzysztof,

On 09/30/2015 02:36 AM, Krzysztof Kozlowski wrote:
> On 29.09.2015 21:42, Javier Martinez Canillas wrote:
>> The Marvell WiFi-Ex driver tries to load a firmware on probe. So if the
>> driver is built-in and probed before a firmware is available, this is
>> not loaded and the chip does not work.
>>
>> This happens for example if an initramfs isn't used since the driver is
>> probed before the root filesystem is mounted.
>>
>> Change the default config since the driver isn't needed for machines to
>> boot and is more convenient to have it enabled as a module to avoid
>> requiring an initramfs or to have the firmware built into the kernel.
>>
>> Signed-off-by: Javier Martinez Canillas <javier@....samsung.com>
>>
>> ---
>>
>>  arch/arm/configs/exynos_defconfig | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> The user-space can always initiate re-probing of device - just re-bind

It is true that you can force a re-probing from user-space by doing:

$ echo "mmc2:0001:1" > /sys/bus/sdio/drivers/mwifiex_sdio/unbind
$ echo "mmc2:0001:1" > /sys/bus/sdio/drivers/mwifiex_sdio/bind

but:

a) This is not obvious. In fact, I didn't think that possibility
before you mentioned and I've been using Linux for many years :)

b) This is not something that isn't done automatically by init systems.

So what users will see is that the driver was probed successfully but
the firmware fails to load later (since the driver users the async
request_firmware_nowait function to request the firmware).

> it. However I assume that driver cannot work without firmware?
>

Yes, it doesn't. I explained this in the commit message. Do you
think it should be made more clear?
 
> Best regards,
> Krzysztof
> 

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America
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