linux-kernel - Re: [PATCH] video: Fix return value of fb_notifier_call

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Date:	Tue, 22 Nov 2011 01:20:27 +0000
From:	Florian Tobias Schandinat <FlorianSchandinat@....de>
To:	Joonyoung Shim <jy0922.shim@...sung.com>
CC:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: Fix return value of fb_notifier_call_chain

On 11/22/2011 12:58 AM, Joonyoung Shim wrote:
> 11/22/2011 08:08 AM, Florian Tobias Schandinat 쓴 글:
>> On 11/21/2011 06:55 AM, Joonyoung Shim wrote:
>>> The return value of blocking_notifier_call_chain isn't errno value, it
>>> is just notify return value. The ret of fb_notifier_call_chain should is
>>> restored to error value from notify return value using
>>> notifier_to_errno().
>> If I'm not wrong this patch would rather break things than fix them. As I
>> understand the notifier_calls would be required to encode the return
>> value with
>> notifier_from_errno. This does not happen at the moment for fb
>> clients, for
>> example fbcon_event_notify in drivers/video/console/fbcon.c, so this
>> patch would
>> screw up the return values, I think.
> 
> OK, but it is wrong to return error value than notify value many
> callback of fb notify clients and some fb notify clients returns notify
> value, please see sh_mobile_lcdc_notify() and sh_hdmi_notify().
> 
> We should use only one, notify value or error value, i think it's right
> to use notify value.

I agree. But all fb clients need to be checked and fixed up if needed at the
same time you do the change you proposed, otherwise things are likely to break.

$ grep -r fb_register_client .
./include/linux/fb.h:extern int fb_register_client(struct notifier_block *nb);
./arch/arm/mach-pxa/am200epd.c: fb_register_client(&am200_fb_notif);
./drivers/leds/ledtrig-backlight.c:     ret = fb_register_client(&n->notifier);
./drivers/video/sh_mobile_hdmi.c:       fb_register_client(&hdmi->notifier);
./drivers/video/fb_notify.c: *  fb_register_client - register a client notifier
./drivers/video/fb_notify.c:int fb_register_client(struct notifier_block *nb)
./drivers/video/fb_notify.c:EXPORT_SYMBOL(fb_register_client);
./drivers/video/console/fbcon.c:        fb_register_client(&fbcon_event_notifier);
./drivers/video/sh_mobile_lcdcfb.c:     fb_register_client(&priv->notifier);
./drivers/video/omap/omapfb_main.c:int omapfb_register_client(struct
omapfb_notifier_block *omapfb_nb,
./drivers/video/omap/omapfb_main.c:EXPORT_SYMBOL(omapfb_register_client);
./drivers/video/omap/omapfb.h:extern int  omapfb_register_client(struct
omapfb_notifier_block *nb,
./drivers/video/backlight/backlight.c:  return fb_register_client(&bd->fb_notif);
./drivers/video/backlight/lcd.c:        return fb_register_client(&ld->fb_notif);
./drivers/staging/olpc_dcon/olpc_dcon.c:
fb_register_client(&dcon->fbevent_nb);

Best regards,

Florian Tobias Schandinat

> 
> Thanks.
> 
>>
>> Best regards,
>>
>> Florian Tobias Schandinat
>>
>>> Signed-off-by: Joonyoung Shim<jy0922.shim@...sung.com>
>>> ---
>>>   drivers/video/fb_notify.c |    4 +++-
>>>   1 files changed, 3 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/video/fb_notify.c b/drivers/video/fb_notify.c
>>> index 74c2da5..49a64a3 100644
>>> --- a/drivers/video/fb_notify.c
>>> +++ b/drivers/video/fb_notify.c
>>> @@ -42,6 +42,8 @@ EXPORT_SYMBOL(fb_unregister_client);
>>>    */
>>>   int fb_notifier_call_chain(unsigned long val, void *v)
>>>   {
>>> -    return blocking_notifier_call_chain(&fb_notifier_list, val, v);
>>> +    int ret = blocking_notifier_call_chain(&fb_notifier_list, val, v);
>>> +
>>> +    return notifier_to_errno(ret);
>>>   }
>>>   EXPORT_SYMBOL_GPL(fb_notifier_call_chain);
>>
> 
> 

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