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Date:   Wed, 8 Jan 2020 11:08:31 +0100
From:   Sam Ravnborg <sam@ravnborg.org>
To:     Jani Nikula <jani.nikula@intel.com>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Sean Paul <sean@poorly.run>, dri-devel@lists.freedesktop.org,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Emil Velikov <emil.velikov@collabora.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/drm_panel: fix export of drm_panel_of_backlight, try
 #3
Message-ID: <20200108100831.GA23308@ravnborg.org>
References: <20200107203231.920256-1-arnd@arndb.de>
 <87zheyqnla.fsf@intel.com>
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Hi Jani.

On Wed, Jan 08, 2020 at 11:55:29AM +0200, Jani Nikula wrote:
> On Tue, 07 Jan 2020, Arnd Bergmann <arnd@arndb.de> wrote:
> > Making this IS_REACHABLE() was still wrong, as that just determines
> > whether the lower-level backlight code would be reachable from the panel
> > driver. However, with CONFIG_DRM=y and CONFIG_BACKLIGHT_CLASS_DEVICE=m,
> > the drm_panel_of_backlight is left out of drm_panel.o but the condition
> > tells the driver that it is there, leading to multiple link errors such as
> >
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-sitronix-st7701.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-sharp-ls043t1le01.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-seiko-43wvf1g.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-ronbo-rb070d30.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-rocktech-jh057n00900.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-panasonic-vvx10f034n00.ko] undefined!
> > ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-osd-osd101t2587-53ts.ko] undefined!
> >
> > Change the condition to check for whether the function was actually part
> > of the drm module. This version of the patch survived a few hundred
> > randconfig builds, so I have a good feeling this might be the last
> > one for the export.
> 
> Broken record, this will still be wrong, even if it builds and links. No
> backlight support for panel despite expectations.
> 
> See http://mid.mail-archive.com/87d0cnynst.fsf@intel.com
> 
> All of this is just another hack until the backlight config usage is
> fixed for good. Do we really want to make this the example to copy paste
> wherever we hit the issue next?
> 
> I'm not naking, but I'm not acking either.

I will try to take a look at your old BACKLIGHT_CLASS_DEVICE patch this
weekend. I think we need that one fixed - and then we can have this mess
with "drm_panel_of_backlight" fixed in the right way.

Sigh...

	Sam