[PATCH] drm/cma-helper: Add multi buffer support for cma fbdev

[Xinliang Liu]

This patch add a config to support to create multi buffer for cma fbdev. Such as
double buffer and triple buffer.

Cma fbdev is convient to add a legency fbdev. And still many Android devices use
fbdev now and at least double buffer is needed for these Android devices, so
that a buffer flip can be operated. It will need some time for Android device
vendors to abondon legency fbdev. So multi buffer for fbdev is needed.

Signed-off-by: Xinliang Liu <xinliang.liu at linaro.org>
---
 drivers/gpu/drm/Kconfig             | 8 ++++++++
 drivers/gpu/drm/drm_fb_cma_helper.c | 8 +++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 1a0a8df..577f790 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -97,6 +97,14 @@ config DRM_KMS_CMA_HELPER
 	help
 	  Choose this if you need the KMS CMA helper functions
 
+config DRM_CMA_FBDEV_BUFFER_NUM
+	int "Cma Fbdev Buffer Number"
+	depends on DRM_KMS_CMA_HELPER
+	default 1
+	help
+	  Defines the buffer number of cma fbdev.  Default is one buffer.
+	  For double buffer please set to 2 and 3 for triple buffer.
+
 source "drivers/gpu/drm/i2c/Kconfig"
 
 config DRM_TDFX
diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index c19a625..26051b8 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -25,6 +25,12 @@
 #include <drm/drm_fb_cma_helper.h>
 #include <linux/module.h>
 
+#ifdef CONFIG_DRM_CMA_FBDEV_BUFFER_NUM
+#define FBDEV_BUFFER_NUM CONFIG_DRM_CMA_FBDEV_BUFFER_NUM
+#else
+#define FBDEV_BUFFER_NUM 1
+#endif
+
 struct drm_fb_cma {
 	struct drm_framebuffer		fb;
 	struct drm_gem_cma_object	*obj[4];
@@ -253,7 +259,7 @@ static int drm_fbdev_cma_create(struct drm_fb_helper *helper,
 	bytes_per_pixel = DIV_ROUND_UP(sizes->surface_bpp, 8);
 
 	mode_cmd.width = sizes->surface_width;
-	mode_cmd.height = sizes->surface_height;
+	mode_cmd.height = sizes->surface_height * FBDEV_BUFFER_NUM;
 	mode_cmd.pitches[0] = sizes->surface_width * bytes_per_pixel;
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 		sizes->surface_depth);
-- 
1.9.1