linux-kernel - Re: [RFC PATCH] video/logo: introduce new system state for checking if logos are freed

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Message-ID: <55641E1E.9010607@denx.de>
Date:	Tue, 26 May 2015 09:17:50 +0200
From:	Heiko Schocher <hs@...x.de>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
CC:	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-fbdev@...r.kernel.org,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>
Subject: Re: [RFC PATCH] video/logo: introduce new system state for checking
 if logos are freed

Hello Tomi,

Am 26.05.2015 08:54, schrieb Tomi Valkeinen:
>
>
> On 26/05/15 06:56, Heiko Schocher wrote:
>
>>> Without locking, the initmem may be freed while fb_find_logo() is
>>> running.
>>
>> Yes, you are right, that must be added ... but has such a change a
>> chance to go in mainline?
>
> I don't know. To be honest, this whole thing feels a bit like hackery. I

Full Ack ;-)

> think initdata should only be accessed from initcalls, never asynchronously.

Yes.

>> BTW: Could this not be currently a problem on multicore systems?
>> If lets say core 2 just draws the logo, another core 1 calls
>> fb_logo_late_init() and later core 1 free_initmem(), while the core 2
>> still draws it?
>
> Yes, I think so...
>
> So, maybe it would be better to not even try to go forward with the
> current approach. Two approaches come to my mind:
>
> 1) Keep the logos in the memory, and don't even try to free them. I
> don't know many bytes they are in total, though.

That was my first thought too... but we waste memory ... not nice.

> 2) Make a copy of the logos to a kmalloced area at some early boot
> stage. Then manually free the logos at some point (after the first
> access to the logos? after a certain time (urgh...)?).

maybe yes ... or  ...

3) wait for all cores, until they reached SYSTEM_FREEING_MEM and
free init mem only than? But are all cores used/started when booting?

4) draw only one logo even on multicores ... why must every core draw
a logo? Currently each core draws the logo, and on a system with more
than 4 cores, I think this looks not really good ...

Hmm... I do not really have a lot experience in this area ... but why
is the logo only drawed when booting? Is there nothing like a "redraw"
of it?

Maybe others have here a good idea?

bye,
Heiko
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