linux-kernel - Re: [PATCH v3 3/3] console/fbcon: Add support for deferred console takeover

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Date:   Tue, 26 Jun 2018 20:29:44 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] console/fbcon: Add support for deferred console
 takeover

Hi,

On 26-06-18 19:12, Andy Shevchenko wrote:
> On Tue, Jun 26, 2018 at 4:55 PM, Hans de Goede <hdegoede@...hat.com> wrote:
>> Currently fbcon claims fbdevs as soon as they are registered and takes over
>> the console as soon as the first fbdev gets registered.
>>
>> This behavior is undesirable in cases where a smooth graphical bootup is
>> desired, in such cases we typically want the contents of the framebuffer
>> (typically a vendor logo) to stay in place as is.
>>
>> The current solution for this problem (on embedded systems) is to not
>> enable fbcon.
>>
>> This commit adds a new FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER config option,
>> which when enabled defers fbcon taking over the console from the dummy
>> console until the first text is displayed on the console. Together with the
>> "quiet" kernel commandline option, this allows fbcon to still be used
>> together with a smooth graphical bootup, having it take over the console as
>> soon as e.g. an error message is logged.
> 
>> +       for (i = 0; i < FB_MAX; i++) {
>> +               if (registered_fb[i])
>> +                       fbcon_fb_registered(registered_fb[i]);
>> +       }
> 
> Simple git grep shows that we perhaps do
> 
> #define for_each_registered_fbcon(i) ...
> 
> (As an example see for_each_pci_bridge() how it's done there)

This is probably a worthwhile cleanup for all the fbdev related
code / drivers. But outside of the scope of this patchset.

Regards,

Hans