linux-kernel - Re: [PATCH] omapfb: In omapfb_probe return -EPROBE_DEFER when display driver is not loaded yet

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Date:	Tue, 23 Jul 2013 13:01:39 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Pavel Machek <pavel@....cz>,
	Pali Rohár <pali.rohar@...il.com>
CC:	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	<linux-omap@...r.kernel.org>, <linux-fbdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] omapfb: In omapfb_probe return -EPROBE_DEFER when display
 driver is not loaded yet

On 13/07/13 21:27, Pavel Machek wrote:
> On Wed 2013-07-10 15:08:59, Pali Rohár wrote:
>> * On RX-51 probing for acx565akm driver is later then for omapfb which cause that omapfb probe fail and framebuffer is not working
>> * EPROBE_DEFER causing that kernel try to probe for omapfb later again which fixing this problem
>>
>> * Without this patch display on Nokia RX-51 (N900) phone not working
>>
>> Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> 
> Tested-by: Pavel Machek <pavel@....cz>

Which kernel version is this? Does it have
dfbc32316c6991010328c21e6046b05bac57eb84 (OMAPFB: defer probe if no displays)?

Then again, rx51 has tv-output, which probably gets probed early. So omapfb
does see one functional display, and starts, even if the LCD is not available
yet.

> (Actually, do we know which commit broke the ordering? We may want to
> simply revert that one...)

Well, my understand that this is how it's supposed to work. There's no defined
order with the driver probes, and the drivers just have to deal with their
dependencies not being there yet.

I don't have a perfect solution for this problem for omapfb. omapfb doesn't
support dynamically adding displays, so all the displays it uses have to be
probed before omapfb. And omapfb doesn't know which displays will be probed.

The patch below was added for 3.11. Does it fix the issue for you? Perhaps it
should be added for 3.10 also.

 Tomi

commit e9f322b4913e5d3e5c5d21dc462ca6f8a86e1df1
Author: Tomi Valkeinen <tomi.valkeinen@...com>
Date:   Thu May 23 16:41:25 2013 +0300

    OMAPFB: use EPROBE_DEFER if default display is not present
    
    Currently omapfb returns EPROBE_DEFER if no displays have been probed at
    the time omapfb is probed. However, sometimes some of the displays have
    been probed at that time, but not all. We can't return EPROBE_DEFER in
    that case, because then one missing driver would cause omapfb to defer
    always, preventing any display from working.
    
    However, if the user has defined a default display, we can presume that
    the driver for that display is eventually loaded. Thus, this patch
    changes omapfb to return EPROBE_DEFER in case default display is not
    found.
    
    Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>

diff --git a/drivers/video/omap2/omapfb/omapfb-main.c b/drivers/video/omap2/omapfb/omapfb-main.c
index 528e453..27d6905 100644
--- a/drivers/video/omap2/omapfb/omapfb-main.c
+++ b/drivers/video/omap2/omapfb/omapfb-main.c
@@ -2503,7 +2503,7 @@ static int omapfb_probe(struct platform_device *pdev)
 
        if (def_display == NULL) {
                dev_err(fbdev->dev, "failed to find default display\n");
-               r = -EINVAL;
+               r = -EPROBE_DEFER;
                goto cleanup;
        }



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