atmel_lcdfb: backlight control

On the sam9 EK boards, the LCD backlight is hooked up to a PWM output from
the LCD controller.  It's controlled by "contrast" registers though.

This patch lets boards declare that they have that kind of backlight
control.  The driver can then export this control, letting screenblank and
other operations actually take effect ...  reducing the typically
substantial power drain from the backlight.

Note that it's not fully cooked
  - doesn't force backlight off during system suspend
  - the "power" and "blank" events may not be done right
This should be easily added in the future.

[nicolas.ferre@atmel.com: remove unneeded inline and rename functions]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 111 insertions, 4 deletions

diff --git a/drivers/video/atmel_lcdfb.c b/drivers/video/atmel_lcdfb.c
index 5d22ea532e42..fc65c02306dd 100644
--- a/drivers/video/atmel_lcdfb.c
+++ b/drivers/video/atmel_lcdfb.c
@@ -16,6 +16,7 @@
 #include <linux/fb.h>
 #include <linux/init.h>
 #include <linux/delay.h>
+#include <linux/backlight.h>
 
 #include <asm/arch/board.h>
 #include <asm/arch/cpu.h>
@@ -69,6 +70,107 @@ static void atmel_lcdfb_update_dma2d(struct atmel_lcdfb_info *sinfo,
 }
 #endif
 
+static const u32 contrast_ctr = ATMEL_LCDC_PS_DIV8
+                | ATMEL_LCDC_POL_POSITIVE
+                | ATMEL_LCDC_ENA_PWMENABLE;
+
+#ifdef CONFIG_BACKLIGHT_ATMEL_LCDC
+
+/* some bl->props field just changed */
+static int atmel_bl_update_status(struct backlight_device *bl)
+{
+        struct atmel_lcdfb_info *sinfo = bl_get_data(bl);
+        int                     power = sinfo->bl_power;
+        int                     brightness = bl->props.brightness;
+
+        /* REVISIT there may be a meaningful difference between
+         * fb_blank and power ... there seem to be some cases
+         * this doesn't handle correctly.
+         */
+        if (bl->props.fb_blank != sinfo->bl_power)
+                power = bl->props.fb_blank;
+        else if (bl->props.power != sinfo->bl_power)
+                power = bl->props.power;
+
+        if (brightness < 0 && power == FB_BLANK_UNBLANK)
+                brightness = lcdc_readl(sinfo, ATMEL_LCDC_CONTRAST_VAL);
+        else if (power != FB_BLANK_UNBLANK)
+                brightness = 0;
+
+        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_VAL, brightness);
+        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_CTR,
+                        brightness ? contrast_ctr : 0);
+
+        bl->props.fb_blank = bl->props.power = sinfo->bl_power = power;
+
+        return 0;
+}
+
+static int atmel_bl_get_brightness(struct backlight_device *bl)
+{
+        struct atmel_lcdfb_info *sinfo = bl_get_data(bl);
+
+        return lcdc_readl(sinfo, ATMEL_LCDC_CONTRAST_VAL);
+}
+
+static struct backlight_ops atmel_lcdc_bl_ops = {
+        .update_status = atmel_bl_update_status,
+        .get_brightness = atmel_bl_get_brightness,
+};
+
+static void init_backlight(struct atmel_lcdfb_info *sinfo)
+{
+        struct backlight_device *bl;
+
+        sinfo->bl_power = FB_BLANK_UNBLANK;
+
+        if (sinfo->backlight)
+                return;
+
+        bl = backlight_device_register("backlight", &sinfo->pdev->dev,
+                        sinfo, &atmel_lcdc_bl_ops);
+        if (IS_ERR(sinfo->backlight)) {
+                dev_err(&sinfo->pdev->dev, "error %ld on backlight register\n",
+                                PTR_ERR(bl));
+                return;
+        }
+        sinfo->backlight = bl;
+
+        bl->props.power = FB_BLANK_UNBLANK;
+        bl->props.fb_blank = FB_BLANK_UNBLANK;
+        bl->props.max_brightness = 0xff;
+        bl->props.brightness = atmel_bl_get_brightness(bl);
+}
+
+static void exit_backlight(struct atmel_lcdfb_info *sinfo)
+{
+        if (sinfo->backlight)
+                backlight_device_unregister(sinfo->backlight);
+}
+
+#else
+
+static void init_backlight(struct atmel_lcdfb_info *sinfo)
+{
+        dev_warn(&sinfo->pdev->dev, "backlight control is not available\n");
+}
+
+static void exit_backlight(struct atmel_lcdfb_info *sinfo)
+{
+}
+
+#endif
+
+static void init_contrast(struct atmel_lcdfb_info *sinfo)
+{
+        /* have some default contrast/backlight settings */
+        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_CTR, contrast_ctr);
+        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_VAL, ATMEL_LCDC_CVAL_DEFAULT);
+
+        if (sinfo->lcdcon_is_backlight)
+                init_backlight(sinfo);
+}
+
 
 static struct fb_fix_screeninfo atmel_lcdfb_fix __initdata = {
         .type           = FB_TYPE_PACKED_PIXELS,
@@ -390,10 +492,6 @@ static int atmel_lcdfb_set_par(struct fb_info *info)
         /* Disable all interrupts */
         lcdc_writel(sinfo, ATMEL_LCDC_IDR, ~0UL);
 
-        /* Set contrast */
-        value = ATMEL_LCDC_PS_DIV8 | ATMEL_LCDC_POL_POSITIVE | ATMEL_LCDC_ENA_PWMENABLE;
-        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_CTR, value);
-        lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_VAL, ATMEL_LCDC_CVAL_DEFAULT);
         /* ...wait for DMA engine to become idle... */
         while (lcdc_readl(sinfo, ATMEL_LCDC_DMACON) & ATMEL_LCDC_DMABUSY)
                 msleep(10);
@@ -597,6 +695,7 @@ static int __init atmel_lcdfb_probe(struct platform_device *pdev)
                 sinfo->default_monspecs = pdata_sinfo->default_monspecs;
                 sinfo->atmel_lcdfb_power_control = pdata_sinfo->atmel_lcdfb_power_control;
                 sinfo->guard_time = pdata_sinfo->guard_time;
+                sinfo->lcdcon_is_backlight = pdata_sinfo->lcdcon_is_backlight;
         } else {
                 dev_err(dev, "cannot get default configuration\n");
                 goto free_info;
@@ -690,6 +789,9 @@ static int __init atmel_lcdfb_probe(struct platform_device *pdev)
                 goto release_mem;
         }
 
+        /* Initialize PWM for contrast or backlight ("off") */
+        init_contrast(sinfo);
+
         /* interrupt */
         ret = request_irq(sinfo->irq_base, atmel_lcdfb_interrupt, 0, pdev->name, info);
         if (ret) {
@@ -741,6 +843,7 @@ free_cmap:
 unregister_irqs:
         free_irq(sinfo->irq_base, info);
 unmap_mmio:
+        exit_backlight(sinfo);
         iounmap(sinfo->mmio);
 release_mem:
         release_mem_region(info->fix.mmio_start, info->fix.mmio_len);
@@ -775,6 +878,7 @@ static int __exit atmel_lcdfb_remove(struct platform_device *pdev)
         if (!sinfo)
                 return 0;
 
+        exit_backlight(sinfo);
         if (sinfo->atmel_lcdfb_power_control)
                 sinfo->atmel_lcdfb_power_control(0);
         unregister_framebuffer(info);
@@ -801,6 +905,9 @@ static int __exit atmel_lcdfb_remove(struct platform_device *pdev)
 
 static struct platform_driver atmel_lcdfb_driver = {
         .remove         = __exit_p(atmel_lcdfb_remove),
+
+// FIXME need suspend, resume
+
         .driver         = {
                 .name   = "atmel_lcdfb",
                 .owner  = THIS_MODULE,