linux-kernel - Re: [PATCH v6 5/5] fbdev: Make registered

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Message-ID: <69d8ad0e-efc6-f37d-9aa7-d06f8de16a6a@redhat.com>
Date:   Thu, 9 Jun 2022 15:09:21 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     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>,
        Sam Ravnborg <sam@...nborg.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: Re: [PATCH v6 5/5] fbdev: Make registered_fb[] private to fbmem.c

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.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat