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Subject[PATCH] drm/ssd130x: Silence a `dubious: x & !y` warning
Date
The sparse tool complains with the following warning:

$ make M=drivers/gpu/drm/solomon/ C=2
CC [M] drivers/gpu/drm/solomon/ssd130x.o
CHECK drivers/gpu/drm/solomon/ssd130x.c
drivers/gpu/drm/solomon/ssd130x.c:363:21: warning: dubious: x & !y

This seems to be a false positive in my opinion but still we can silence
the tool while making the code easier to read. Let's also add a comment,
to explain why the "com_seq" logical not is used rather than its value.

Reported-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
---

drivers/gpu/drm/solomon/ssd130x.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/solomon/ssd130x.c b/drivers/gpu/drm/solomon/ssd130x.c
index c3bf3a18302e..b16330a8b624 100644
--- a/drivers/gpu/drm/solomon/ssd130x.c
+++ b/drivers/gpu/drm/solomon/ssd130x.c
@@ -81,7 +81,7 @@
#define SSD130X_SET_PRECHARGE_PERIOD2_MASK GENMASK(7, 4)
#define SSD130X_SET_PRECHARGE_PERIOD2_SET(val) FIELD_PREP(SSD130X_SET_PRECHARGE_PERIOD2_MASK, (val))
#define SSD130X_SET_COM_PINS_CONFIG1_MASK GENMASK(4, 4)
-#define SSD130X_SET_COM_PINS_CONFIG1_SET(val) FIELD_PREP(SSD130X_SET_COM_PINS_CONFIG1_MASK, !(val))
+#define SSD130X_SET_COM_PINS_CONFIG1_SET(val) FIELD_PREP(SSD130X_SET_COM_PINS_CONFIG1_MASK, (val))
#define SSD130X_SET_COM_PINS_CONFIG2_MASK GENMASK(5, 5)
#define SSD130X_SET_COM_PINS_CONFIG2_SET(val) FIELD_PREP(SSD130X_SET_COM_PINS_CONFIG2_MASK, (val))

@@ -298,6 +298,7 @@ static void ssd130x_power_off(struct ssd130x_device *ssd130x)
static int ssd130x_init(struct ssd130x_device *ssd130x)
{
u32 precharge, dclk, com_invdir, compins, chargepump, seg_remap;
+ bool scan_mode;
int ret;

/* Set initial contrast */
@@ -360,7 +361,13 @@ static int ssd130x_init(struct ssd130x_device *ssd130x)

/* Set COM pins configuration */
compins = BIT(1);
- compins |= (SSD130X_SET_COM_PINS_CONFIG1_SET(ssd130x->com_seq) |
+ /*
+ * The COM scan mode field values are the inverse of the boolean DT
+ * property "solomon,com-seq". The value 0b means scan from COM0 to
+ * COM[N - 1] while 1b means scan from COM[N - 1] to COM0.
+ */
+ scan_mode = !ssd130x->com_seq;
+ compins |= (SSD130X_SET_COM_PINS_CONFIG1_SET(scan_mode) |
SSD130X_SET_COM_PINS_CONFIG2_SET(ssd130x->com_lrremap));
ret = ssd130x_write_cmd(ssd130x, 2, SSD130X_SET_COM_PINS_CONFIG, compins);
if (ret < 0)
--
2.39.0
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