linux-kernel - Mark olpc_dcon BROKEN [Was: [PATCH v6 5/5] fbdev: Make registered

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Date:   Thu, 9 Jun 2022 19:23:28 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        Jerry Lin <wahahab11@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laszlo Ersek <lersek@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>, kvm@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        kernel test robot <lkp@...el.com>,
        Jens Frederich <jfrederich@...il.com>,
        Jon Nettleton <jon.nettleton@...il.com>,
        linux-staging@...ts.linux.dev,
        Daniel Vetter <daniel.vetter@...el.com>,
        Daniel Vetter <daniel@...ll.ch>, Helge Deller <deller@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Alex Deucher <alexander.deucher@....com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        linux-fbdev@...r.kernel.org, Zheyu Ma <zheyuma97@...il.com>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Mark olpc_dcon BROKEN [Was: [PATCH v6 5/5] fbdev: Make
 registered_fb[] private to fbmem.c]

Hi Javier.

On Thu, Jun 09, 2022 at 03:09:21PM +0200, Javier Martinez Canillas wrote:
> Hello Thomas,
> 
> On 6/9/22 13:49, Thomas Zimmermann wrote:
> > Hi Javier
> > 
> > Am 07.06.22 um 20:23 schrieb Javier Martinez Canillas:
> >> From: Daniel Vetter <daniel.vetter@...ll.ch>
> >>
> >> Well except when the olpc dcon fbdev driver is enabled, that thing
> >> digs around in there in rather unfixable ways.
> > 
> > There is fb_client_register() to set up a 'client' on top of an fbdev. 
> > The client would then get messages about modesetting, blanks, removals, 
> > etc. But you'd probably need an OLPC to convert dcon, and the mechanism 
> > itself is somewhat unloved these days.
> > 
> > Your patch complicates the fbdev code AFAICT. So I'd either drop it or, 
> > even better, build a nicer interface for dcon.
> > 
> > The dcon driver appears to look only at the first entry. Maybe add 
> > fb_info_get_by_index() and fb_info_put() and export those. They would be 
> > trivial wrappers somewhere in fbmem.c:
> > 
> > #if IS_ENABLED(CONFIG_FB_OLPC_DCON)
> > struct fb_info *fb_info_get_by_index(unsigned int index)
> > {
> > 	return get_fb_info(index);
> > }
> > EXPORT_SYMBOL()
> > void fb_info_put(struct fb_info *fb_info)
> > {
> > 	put_fb_info(fb_info);
> > }
> > EXPORT_SYMBOL()
> > #endif
> > 
> > In dcon itself, using the new interfaces will actually acquire a 
> > reference to keep the display alive. The code at [1] could be replaced. 
> > And a call to fb_info_put() needs to go into dcon_remove(). [2]
> > 
> 
> Thanks for your suggestions, that makes sense to me. I'll drop this
> patch from the set and post as a follow-up a different approach as
> you suggested.

To repeat myself from irc.
olpc_dcon is a staging driver and we should avoid inventing anything in
core code for to make staging drivers works.
Geert suggested EXPORT_SYMPBOL_NS_GPL() that could work and narrow it
down to olpc_dcon.
The better approach is to mark said driver BROKEN and then someone can
fix it it there is anyone who cares.
Last commit to olpc_dcon was in 2019: e40219d5e4b2177bfd4d885e7b64e3b236af40ac
and maybe Jerry Lin cares enough to fix it.

Added Jerry and Greg to the mail.

	Sam