Re: [PATCH v3] backlight: lm3630a: bump REG_MAX value to 0x50 instead of 0x1F

From: Daniel Thompson
Date: Fri Jun 23 2017 - 05:33:59 EST

On 23/06/17 04:54, Bhushan Shah wrote:
In the lm3630a_chip_init we try to write to 0x50 register, which is
higher value then the max_register value, this resulted in regmap_write
return -EIO.

Fix this by bumping REG_MAX value to 0x50.

This code was introduced with the chip revision in commit 28e64a68a2ef,
however setting filter strength was failing silently because it used
unsigned int for storing and comparing the return values. Bug related to
signedness was fixed in 2a0c316bf3cc, which made it error out correctly
instead of failing silently.

I found this issue by using this driver on LGE Nexus 5 (hammerhead).
After this commit lm3630a_chip_init succeeds instead of failing with

Fixes: 28e64a68a2ef ("backlight: lm3630: apply chip revision")
Fixes: 2a0c316bf3cc ("drivers/video/backlight/lm3630a_bl.c: fix
signedness bug in lm3630a_chip_init()")

Signed-off-by: Bhushan Shah <bshah@xxxxxxx>
Suggested-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>

Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>


Changes since v2:
- Include information about commits which introduced bug in commit message
- Include information about test hardware in commit message
- Expand define name to REG_FILTER_STRENGTH

drivers/video/backlight/lm3630a_bl.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/video/backlight/lm3630a_bl.c b/drivers/video/backlight/lm3630a_bl.c
index 60d6c2ac87aa..2030a6b77a09 100644
--- a/drivers/video/backlight/lm3630a_bl.c
+++ b/drivers/video/backlight/lm3630a_bl.c
@@ -31,7 +31,8 @@
#define REG_FAULT 0x0B
#define REG_PWM_OUTLOW 0x12
#define REG_PWM_OUTHIGH 0x13
-#define REG_MAX 0x1F
+#define REG_MAX 0x50
struct lm3630a_chip {
@@ -80,7 +81,7 @@ static int lm3630a_chip_init(struct lm3630a_chip *pchip)
usleep_range(1000, 2000);
/* set Filter Strength Register */
- rval = lm3630a_write(pchip, 0x50, 0x03);
+ rval = lm3630a_write(pchip, REG_FILTER_STRENGTH, 0x03);
/* set Cofig. register */
rval |= lm3630a_update(pchip, REG_CONFIG, 0x07, pdata->pwm_ctrl);
/* set boost control */