[PATCH] video: imxfb: Do not crash on reboot

[Fabio Estevam]

Issuing a "reboot" command after the LCD times out causes the following
warnings:

Requesting system reboot
------------[ cut here ]------------
WARNING: at drivers/clk/clk.c:471 clk_disable+0x24/0x50()
Modules linked in:
[<c001ad90>] (unwind_backtrace+0x0/0xf4) from [<c0025aac>] (warn_slowpath_common+0x48/0x60)
[<c0025aac>] (warn_slowpath_common+0x48/0x60) from [<c0025ae0>] (warn_slowpath_null+0x1c/0x24)
[<c0025ae0>] (warn_slowpath_null+0x1c/0x24) from [<c03960a0>] (clk_disable+0x24/0x50)
[<c03960a0>] (clk_disable+0x24/0x50) from [<c02695a0>] (imxfb_disable_controller+0x48/0x7c)
[<c02695a0>] (imxfb_disable_controller+0x48/0x7c) from [<c029d838>] (platform_drv_shutdown+0x18/0x1c)
[<c029d838>] (platform_drv_shutdown+0x18/0x1c) from [<c02990fc>] (device_shutdown+0x48/0x14c)
[<c02990fc>] (device_shutdown+0x48/0x14c) from [<c003d09c>] (kernel_restart_prepare+0x2c/0x3c)
[<c003d09c>] (kernel_restart_prepare+0x2c/0x3c) from [<c003d0e4>] (kernel_restart+0xc/0x48)
[<c003d0e4>] (kernel_restart+0xc/0x48) from [<c003d1e8>] (sys_reboot+0xc0/0x1bc)
[<c003d1e8>] (sys_reboot+0xc0/0x1bc) from [<c0014ca0>] (ret_fast_syscall+0x0/0x2c)
---[ end trace da6b502ca79c854f ]---
------------[ cut here ]------------
WARNING: at drivers/clk/clk.c:380 clk_unprepare+0x1c/0x2c()
Modules linked in:
[<c001ad90>] (unwind_backtrace+0x0/0xf4) from [<c0025aac>] (warn_slowpath_common+0x48/0x60)
[<c0025aac>] (warn_slowpath_common+0x48/0x60) from [<c0025ae0>] (warn_slowpath_null+0x1c/0x24)
[<c0025ae0>] (warn_slowpath_null+0x1c/0x24) from [<c0396338>] (clk_unprepare+0x1c/0x2c)
[<c0396338>] (clk_unprepare+0x1c/0x2c) from [<c02695a8>] (imxfb_disable_controller+0x50/0x7c)
[<c02695a8>] (imxfb_disable_controller+0x50/0x7c) from [<c029d838>] (platform_drv_shutdown+0x18/0x1c)
[<c029d838>] (platform_drv_shutdown+0x18/0x1c) from [<c02990fc>] (device_shutdown+0x48/0x14c)
[<c02990fc>] (device_shutdown+0x48/0x14c) from [<c003d09c>] (kernel_restart_prepare+0x2c/0x3c)
[<c003d09c>] (kernel_restart_prepare+0x2c/0x3c) from [<c003d0e4>] (kernel_restart+0xc/0x48)
[<c003d0e4>] (kernel_restart+0xc/0x48) from [<c003d1e8>] (sys_reboot+0xc0/0x1bc)
[<c003d1e8>] (sys_reboot+0xc0/0x1bc) from [<c0014ca0>] (ret_fast_syscall+0x0/0x2c)
---[ end trace da6b502ca79c8550 ]---
------------[ cut here ]------------

This happens because "reboot" triggers imxfb_shutdown(), which calls
imxfb_disable_controller with the clocks already disabled.

To prevent this, add a clock enabled status so that we can check if the clocks
are enabled before disabling them. 

Signed-off-by: Fabio Estevam <fabio.estevam at freescale.com>
---
 drivers/video/imxfb.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/video/imxfb.c b/drivers/video/imxfb.c
index f3363b2..6acf98a 100644
--- a/drivers/video/imxfb.c
+++ b/drivers/video/imxfb.c
@@ -134,6 +134,7 @@ struct imxfb_info {
 	struct clk		*clk_ipg;
 	struct clk		*clk_ahb;
 	struct clk		*clk_per;
+	int			enabled;
 
 	/*
 	 * These are the addresses we mapped
@@ -530,9 +531,12 @@ static void imxfb_enable_controller(struct imxfb_info *fbi)
 	 */
 	writel(RMCR_LCDC_EN_MX1, fbi->regs + LCDC_RMCR);
 
-	clk_prepare_enable(fbi->clk_ipg);
-	clk_prepare_enable(fbi->clk_ahb);
-	clk_prepare_enable(fbi->clk_per);
+	if (!fbi->enabled) {
+		clk_prepare_enable(fbi->clk_ipg);
+		clk_prepare_enable(fbi->clk_ahb);
+		clk_prepare_enable(fbi->clk_per);
+		fbi->enabled = 1;
+	}
 
 	if (fbi->backlight_power)
 		fbi->backlight_power(1);
@@ -551,9 +555,12 @@ static void imxfb_disable_controller(struct imxfb_info *fbi)
 
 	writel(0, fbi->regs + LCDC_RMCR);
 
-	clk_disable_unprepare(fbi->clk_per);
-	clk_disable_unprepare(fbi->clk_ipg);
-	clk_disable_unprepare(fbi->clk_ahb);
+	if (fbi->enabled) {
+		clk_disable_unprepare(fbi->clk_per);
+		clk_disable_unprepare(fbi->clk_ipg);
+		clk_disable_unprepare(fbi->clk_ahb);
+		fbi->enabled = 0;
+	}
 }
 
 static int imxfb_blank(int blank, struct fb_info *info)
-- 
1.7.9.5