On Wed, 6 Aug 2008, Stanislaw Gruszka wrote:
I try to implement double buffering for Atmel LCD display on AT91SAM9263 based
board. I could not find any document about panning display on linux
framebuffer, so I have some question about it and generic question about
double buffer design.
1) Is FBIOPAN_DISPLAY ioctl right way to implement double buffering?
Yes.
2) What is the difference between ypanstep and ywrapstep, which one should be
used for double buffering.
Ypanstep is the allowed step increment for panning vertically.
E.g. for a screen with 200 lines and y.offset = 50, it will display
lines 50-249 of the frame buffer.
Ywrapstep is the allowed step increment for wrapping the screen
vertically.
E.g. for a screen with 200 lines and y.offset = 50, it will display
lines 50-199 followed by lines 0-49 of the frame buffer.
3) Does double buffer stuff should be turned on using module parameter,
compile time parameter, board specific parameter (flag from platform device).
As it consume 2x memory I don't thing anyone want it by default.
No, let userspace ask for it when it specifies a large
fb_var_screeninfo.yres_virtual, if possible. If you have to allocate all
frame buffer memory at initialization time, you can use a board specific
parameter or a kernel command line parameter.
quoted hunk ↗ jump to hunk
diff --git a/drivers/video/atmel_lcdfb.c b/drivers/video/atmel_lcdfb.c
index b004036..d0b2bed 100644
--- a/drivers/video/atmel_lcdfb.c
+++ b/drivers/video/atmel_lcdfb.c
@@ -7,7 +7,6 @@
* License. See the file COPYING in the main directory of this archive for
* more details.
*/
-
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/dma-mapping.h>
@@ -41,6 +40,8 @@
#if defined(CONFIG_ARCH_AT91)
#define ATMEL_LCDFB_FBINFO_DEFAULT FBINFO_DEFAULT
+static int double_buffering = 1;
+
static inline void atmel_lcdfb_update_dma2d(struct atmel_lcdfb_info *sinfo,
struct fb_var_screeninfo *var)
{@@ -789,7 +790,13 @@ static int __init atmel_lcdfb_probe(struct
platform_device *pdev)
* Don't clear the framebuffer -- someone may have set
* up a splash image.
*/
+ double_buffering = 0;
+ dev_info(dev, "dissable double buffering\n");
} else {
+ if (double_buffering) {
+ info->fix.ypanstep = info->var.yres_virtual;
I would set it to 1, if there's no hardware limitation preventing this.
+ info->var.yres_virtual *= 2;
This is done at initialization time, hence it cannot be changed later by
using the ioctls?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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