Re: [PATCH 1/9] backlight: atmel-pwm-bl: fix reported brightness

On Wednesday, October 23, 2013 5:51 PM, Johan Hovold wrote:

On Wed, Oct 23, 2013 at 10:20:59AM +0900, Jingoo Han wrote:

quoted

On Wednesday, October 23, 2013 2:27 AM, Johan Hovold wrote:

quoted

The driver supports 16-bit brightness values, but the value returned
from get_brightness was truncated to eight bits.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <redacted>
---
 drivers/video/backlight/atmel-pwm-bl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/video/backlight/atmel-pwm-bl.c b/drivers/video/backlight/atmel-pwm-bl.c
index 66885fb..8aac273 100644
--- a/drivers/video/backlight/atmel-pwm-bl.c
+++ b/drivers/video/backlight/atmel-pwm-bl.c

@@ -70,7 +70,7 @@ static int atmel_pwm_bl_set_intensity(struct backlight_device *bd)
 static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
 {
 	struct atmel_pwm_bl *pwmbl = bl_get_data(bd);
-	u8 intensity;
+	u32 intensity;

 	if (pwmbl->pdata->pwm_active_low) {
 		intensity = pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -

@@ -80,7 +80,7 @@ static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
 			pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY);
 	}

-	return intensity;
+	return (u16)intensity;

However, atmel_pwm_bl_get_intensity() should return 'int',
instead of 'u16'.

Yes, but the cast to int is implicit. Perhaps

	return (intensity & 0xffff);

(or just a comment) would make it more clear why the cast is there.

quoted

Also, pwm_channel_readl() returns 'u32'.

Yes, (and only the 16 least-significant bits are used). That and the
fact that the platform-data limits are currently unsigned long (I was
considering fixing this later) was why I preferred keeping all register
value manipulation in u32 and do a single cast at the end.

quoted

Then, how about the following?

--- a/drivers/video/backlight/atmel-pwm-bl.c
+++ b/drivers/video/backlight/atmel-pwm-bl.c

@@ -70,17 +70,17 @@ static int atmel_pwm_bl_set_intensity(struct backlight_device *bd)
 static int atmel_pwm_bl_get_intensity(struct backlight_device *bd)
 {

	struct atmel_pwm_bl *pwmbl = bl_get_data(bd);
-	u8 intensity;
+	u16 intensity;

	if (pwmbl->pdata->pwm_active_low) {
-		intensity = pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -
+		intensity = (u16) pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY) -
			pwmbl->pdata->pwm_duty_min;

This would actually introduce a new conversion warning (unless you add
parentheses as well) as pwm_duty_min is unsigned long. Same below.

quoted

	} else {
-		intensity = pwmbl->pdata->pwm_duty_max -
+		intensity = (u16) pwmbl->pdata->pwm_duty_max -
			pwm_channel_readl(&pwmbl->pwmc, PWM_CDTY);
	}

-	return intensity;
+	return (int)intensity;
 }

However, if you feel strongly about this, I'll respin the series (a later
patch would likely no longer apply), use u16 and add casts to the two
assignments.

Thank you for your kind and detailed description. :-)
OK, I have no objection on your original patch.

Would you re-send these patches with my Acked-by with CC'ing  Andrew Morton,
Tomi Valkeinen? Then, these patches can be merged through mm-tree.

Best regards,
Jingoo Han