[PATCH v2 1/2] drm/cma-helper: Add multi buffer support for cma fbdev

[Maxime Ripard]

From: Xinliang Liu <xinliang.liu@xxxxxxxxxx>

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@xxxxxxxxxx>
[s.christ@xxxxxxxxx: Picking patch from
                     https://lkml.org/lkml/2015/9/14/188]
Signed-off-by: Stefan Christ <s.christ@xxxxxxxxx>
Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>
---
 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 ebfe8404c25f..2ca9bb26a4e4 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -121,6 +121,14 @@ 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"
 
 source "drivers/gpu/drm/arm/Kconfig"
diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
index 81b3558302b5..e3f8b9e720a0 100644
--- a/drivers/gpu/drm/drm_fb_cma_helper.c
+++ b/drivers/gpu/drm/drm_fb_cma_helper.c
@@ -411,6 +411,12 @@ static void drm_fbdev_cma_defio_fini(struct fb_info *fbi)
 	kfree(fbi->fbops);
 }
 
+static int fbdev_num_buffers = CONFIG_DRM_CMA_FBDEV_BUFFER_NUM;
+module_param(fbdev_num_buffers, int, 0444);
+MODULE_PARM_DESC(fbdev_num_buffers,
+		 "Number of frame buffers to allocate [default="
+		 __MODULE_STRING(CONFIG_DRM_CMA_FBDEV_BUFFER_NUM) "]");
+
 /*
  * For use in a (struct drm_fb_helper_funcs *)->fb_probe callback function that
  * needs custom struct drm_framebuffer_funcs, like dirty() for deferred_io use.
@@ -437,7 +443,7 @@ int drm_fbdev_cma_create_with_funcs(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_num_buffers;
 	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);
-- 
git-series 0.8.11