linux-kernel - Re: [PATCH] drm: panel: fix excessive stack usage in td028ttec1

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Message-ID: <20200107220019.GC7869@pendragon.ideasonboard.com>
Date:   Wed, 8 Jan 2020 00:00:19 +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@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: panel: fix excessive stack usage in
 td028ttec1_prepare

Hi Arnd,

Thank you for the patch.

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 ?

> ---
>  drivers/gpu/drm/panel/panel-tpo-td028ttec1.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-tpo-td028ttec1.c b/drivers/gpu/drm/panel/panel-tpo-td028ttec1.c
> index cf29405a2dbe..17ee5e87141f 100644
> --- a/drivers/gpu/drm/panel/panel-tpo-td028ttec1.c
> +++ b/drivers/gpu/drm/panel/panel-tpo-td028ttec1.c
> @@ -105,7 +105,7 @@ static int jbt_ret_write_0(struct td028ttec1_panel *lcd, u8 reg, int *err)
>  	return ret;
>  }
>  
> -static int jbt_reg_write_1(struct td028ttec1_panel *lcd,
> +static int noinline_for_stack jbt_reg_write_1(struct td028ttec1_panel *lcd,
>  			   u8 reg, u8 data, int *err)
>  {
>  	struct spi_device *spi = lcd->spi;

-- 
Regards,

Laurent Pinchart