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Date: Wed, 8 Jan 2020 00:12:22 +0200 From: Laurent Pinchart <laurent.pinchart@...asonboard.com> To: Arnd Bergmann <arnd@...db.de> Cc: Thierry Reding <thierry.reding@...il.com>, David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>, Oleksandr Natalenko <oleksandr@...hat.com>, Sam Ravnborg <sam@...nborg.org>, Linus Walleij <linus.walleij@...aro.org>, Boris Brezillon <boris.brezillon@...labora.com>, Tomi Valkeinen <tomi.valkeinen@...com>, dri-devel <dri-devel@...ts.freedesktop.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] drm: panel: fix excessive stack usage in td028ttec1_prepare Hi Arnd, On Tue, Jan 07, 2020 at 11:09:13PM +0100, Arnd Bergmann wrote: > On Tue, Jan 7, 2020 at 11:00 PM Laurent Pinchart wrote: > > On Tue, Jan 07, 2020 at 10:27:33PM +0100, Arnd Bergmann wrote: > > > With gcc -O3, the compiler can inline very aggressively, > > > leading to rather large stack usage: > > > > > > drivers/gpu/drm/panel/panel-tpo-td028ttec1.c: In function 'td028ttec1_prepare': > > > drivers/gpu/drm/panel/panel-tpo-td028ttec1.c:233:1: error: the frame size of 2768 bytes is larger than 2048 bytes [-Werror=frame-larger-than=] > > > } > > > > > > Marking jbt_reg_write_1() as noinline avoids the case where > > > multiple instances of this function get inlined into the same > > > stack frame and each one adds a copy of 'tx_buf'. > > > > > > Fixes: mmtom ("init/Kconfig: enable -O3 for all arches") > > > Signed-off-by: Arnd Bergmann <arnd@...db.de> > > > > Isn't this something that should be fixed at the compiler level ? > > I suspect but have not verified that structleak gcc plugin is partly at > fault here as well, it has caused similar problems elsewhere. > > If you like I can try to dig deeper before that patch gets merged, > and explain more in the changelog or open a gcc bug if necessary. I think we'll need to merge this in the meantime, but if gcc is able to detect too large frame sizes, I think it should have the ability to take a frame size limit into account when optimizing. I haven't checked if this is already possible and just not honoured here (possibly due to a bug) or if the feature is entirely missing. In any case we'll likely have to live with this compiler issue for quite some time. -- Regards, Laurent Pinchart
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