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From: Aaro Koskinen <aaro.koskinen@iki.fi>
To: "Pali Rohár" <pali.rohar@gmail.com>
Cc: "Pavel Machek" <pavel@ucw.cz>,
	sre@kernel.org, "kernel list" <linux-kernel@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-omap@vger.kernel.org, tony@atomide.com, khilman@kernel.org,
	ivo.g.dimitrov.75@gmail.com, patrikbachan@gmail.com,
	serge@hallyn.com, abcloriens@gmail.com, clayton@craftyguy.net,
	martijn@brixit.nl, sakari.ailus@linux.intel.com,
	"Filip Matijević" <filip.matijevic.pz@gmail.com>,
	"Thorsten Leemhuis" <regressions@leemhuis.info>
Subject: Re: v4.17-rc1: regressions on N900, N950
Date: Tue, 22 May 2018 22:41:39 +0300	[thread overview]
Message-ID: <20180522194139.GB2299@darkstar.musicnaut.iki.fi> (raw)
In-Reply-To: <20180522080250.4fzyvqrgw5oigexn@pali>

Hi,

On Tue, May 22, 2018 at 10:02:50AM +0200, Pali Rohár wrote:
> Hi! I remember that in time of migration from platform board code to
> device tree structures there appeared some bug which caused that
> sometimes display were not initialized. And somebody figured out that
> display initialization is failing when some other SPI devices are
> initialized before or after display... This behavior was observed only
> on real N900 hardware, not in qemu.

Touchscreen needs to be initialized before display. This is documented
in the DTS, see arch/arm/boot/dts/omap3-n900.dts:

	* For some reason, touchscreen is necessary for screen to work at
	* all on real hw. It works well without it on emulator.
	*
	* Also... order in the device tree actually matters here.

> Real reason was never explained. In old platform board code there was
> hardcoded order of SPI devices in which initialization happened. And in
> device tree it is probably in (pseudo)-random order. Enabling/disabling
> various config option can affect some timings and order in which kernel
> starts probing and initializing devices...

The issue was also somewhat present with platform/board code, see e.g.
commit e65f131a14726e5f1b880a528271a52428e5b3a5.

My device worked with v4.17-rc1 (haven't found time to test newer kernels),
but if you say the probe order is random then we must find some proper way
to express the dependency.

A.

  reply	other threads:[~2018-05-22 19:41 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-22  7:42 Pavel Machek
2018-04-23 20:29 ` Aaro Koskinen
2018-05-21 21:39   ` Pavel Machek
2018-05-22  8:02     ` Pali Rohár
2018-05-22 19:41       ` Aaro Koskinen [this message]
2018-05-22 20:58         ` Pavel Machek
2018-05-22 21:56           ` Aaro Koskinen
2018-05-23 14:06             ` Pavel Machek
2018-05-23 20:12               ` Pavel Machek
2018-05-23 22:04                 ` Tony Lindgren
2018-05-24  9:23                   ` Pavel Machek
2018-05-24  9:47                   ` Pavel Machek
2018-05-29 20:45                     ` Pavel Machek
2018-05-29 21:09                       ` Sebastian Reichel
2018-05-29 22:34                         ` Pavel Machek
2018-05-23 22:02             ` Aaro Koskinen
2018-05-24  6:25               ` Tomi Valkeinen

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