linux-kernel - [PATCH] fixed sparkling issue on lcd panel when fb

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Date:	Fri, 19 Mar 2010 13:36:50 +0900
From:	InKi Dae <daeinki@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Purdie <rpurdie@...ux.intel.com>,
	Pavel Machek <pavel@....cz>,
	Kyungmin Park <kmpark@...radead.org>,
	linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: [PATCH] fixed sparkling issue on lcd panel when fb_blank mode is 
	changed.

Hello all,

I am sending a e-mail about fb_blank issue.

This issue is a problem that lcd panel is spakled when fb_blank mode is changed
>From FB_BLANK_UNBLANK to FB_BLANK_POWER or FB_BLANK_POWER to FB_BLANK_UNBLANK.

In case of FB_BLANK_UNBLANK, screen = on, vsync = on, hsync = on and
For FB_BLANK_POWERDOWN screen = blanked, vsync = off, hsync = off
So like this when fb_blank mode becomes FB_BLANK_POWERDOWN,
Display controller and lcd panel should become off to reduce power consumption.

Let's see fb_blank function of fbmem.c file.

fb_blank()
{
    if (info->fbops->fb_blank)
            ret = info->fbops->fb_blank(blank, info(
    if (!ret)
            fb_notifier_call_chain(FB_EVENT_BLANK, &event);
}

This problem is because this code calls fb_blank (fb_blank of device
specific framebuffer driver)
Earlier then fb_notifier_call_chain.

For example,
Device specific fb_blank function is registered to generic framebuffer
driver through register_framebuffer function
And fb_notifier_call_chain calls any callback function registered to
lcd class(lcd.c) through fb_notifier_callback function.
So if fb_blank mode is changed to FB_BLANK_POWERDOWN then display
controller would become off(clock disable)
On the other hand, lcd panel would still be on. at this time, some
situation on lcd panel occers like sparkling
Because video clock to be delivered to ldi module of lcd panel is disabled also.

This patch get fb_notifier_call_chain to be called earlier then fb_blank.
Please, review this patch.

signed-off-by : InKi Dae <inki.dae@...sung.com>

Best Regards,
InKi Dae.

Download attachment "fbmem.patch" of type "application/octet-stream" (1089 bytes)