linux-kernel - [PATCH] drm/layerscape: reduce excessive stack usage

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Date:	Mon, 22 Feb 2016 22:33:31 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Alison Wang <b18965@...escale.com>,
	Jianwei Wang <jianwei.wang.chn@...il.com>,
	Alison Wang <alison.wang@...escale.com>,
	David Airlie <airlied@...ux.ie>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>,
	Xiubo Li <lixiubo@...s.chinamobile.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/layerscape: reduce excessive stack usage

The fsl-dcu driver copies a drm_mode_config object to its
stack but then only accesses a single member (dpms_property)
once. The data structure is large enough to trigger a warning
about the amount of kernel stack being used:

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c: In function 'fsl_dcu_drm_connector_create':
drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c:182:1: error: the frame size of 1040 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

This changes the fsl_dcu_drm_connector_create() function to
only access the drm_mode_config by reference, which is also
more efficient.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Fixes: 109eee2f2a18 ("drm/layerscape: Add Freescale DCU DRM driver")
---
 drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c
index 8780deba5e8a..92149152db44 100644
--- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c
+++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_rgb.c
@@ -131,7 +131,7 @@ int fsl_dcu_drm_connector_create(struct fsl_dcu_drm_device *fsl_dev,
 				 struct drm_encoder *encoder)
 {
 	struct drm_connector *connector = &fsl_dev->connector.base;
-	struct drm_mode_config mode_config = fsl_dev->drm->mode_config;
+	struct drm_mode_config *mode_config = &fsl_dev->drm->mode_config;
 	struct device_node *panel_node;
 	int ret;
 
@@ -153,7 +153,7 @@ int fsl_dcu_drm_connector_create(struct fsl_dcu_drm_device *fsl_dev,
 		goto err_sysfs;
 
 	drm_object_property_set_value(&connector->base,
-				      mode_config.dpms_property,
+				      mode_config->dpms_property,
 				      DRM_MODE_DPMS_OFF);
 
 	panel_node = of_parse_phandle(fsl_dev->np, "fsl,panel", 0);
-- 
2.7.0