linux-kernel - Re: [RFC PATCH arm: initial TI-Nspire support]

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Message-Id: <29D8E742-C870-45AE-B102-13A477AE6419@gmail.com>
Date:	Tue, 9 Apr 2013 15:59:52 +1000
From:	Daniel Tang <dt.tangr@...il.com>
To:	Fabian Vogt <fabian@...ter-vogt.de>
Cc:	"Arnd Bergmann" <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, linux@....linux.org.uk,
	"Lionel Debroux" <lionel_debroux@...oo.fr>,
	linux-kernel@...r.kernel.org,
	"Linus Walleij" <linus.walleij@...aro.org>
Subject: Re: [RFC PATCH arm: initial TI-Nspire support]

On 09/04/2013, at 5:16 AM, Fabian Vogt <fabian@...ter-vogt.de> wrote:

> The latest kernel it seems to get stuck at
> console_lock() in register_framebuffer (drivers/video/fbmem.c:1655)
> if the LCD-controller is enabled. (Early printk and serial console works fine)
> CONFIG_NO_HZ is not activated, it works completely.
> Could this be a kernel bug or is this an issue with our timer configuration?

Even with the CONFIG_NO_HZ option disabled, I've found that probing of our LCD hardware sometimes still fail with an error of -2.

Depending on how I arrange the device tree or the contents of the boot arguments or, as said, the CONFIG_NO_HZ option, I get different behaviours ranging from: 
 * Getting a -2 error during device probe (possibly due to a clock not being found).
 * LCD hardware is found but boot hangs right after the driver is initialised.
 * LCD hardware is apparently initialised correctly and text appears onscreen but user mode init hangs and I never get to a shell prompt.

This smells of a race condition that occurs before the clcd driver even gets to initialise. Some bug in our timer code? A OF or console bug perhaps? Though, I'm a bit hesitant to blame it on a kernel subsystem bug until it's clear that our code isn't at fault.

Any suggestions?--
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