linux-kernel - [PATCH v2 5/7] bu27034: ROHM BU27034ANUC correct gains and times

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Message-ID: <19f8cca2b5498fbfea6e657b7b9c90b78516866a.1720176341.git.mazziesaccount@gmail.com>
Date: Fri, 5 Jul 2024 13:55:19 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
	Matti Vaittinen <mazziesaccount@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Matti Vaittinen <mazziesaccount@...il.com>,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/7] bu27034: ROHM BU27034ANUC correct gains and times

The ROHM BU27034NUC was cancelled and BU27034ANUC is replacing this
sensor. The BU27034ANUC does not support all the gains or all the
integration times that were supported on BU27034NUC.

Srop unsupported times and gains

Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
---
Revision history:
v1 => v2:
 - splitted from a big patch, no real changes
---
 drivers/iio/light/rohm-bu27034.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/drivers/iio/light/rohm-bu27034.c b/drivers/iio/light/rohm-bu27034.c
index 86b8771caff0..850ec78f5405 100644
--- a/drivers/iio/light/rohm-bu27034.c
+++ b/drivers/iio/light/rohm-bu27034.c
@@ -94,49 +94,39 @@ static const unsigned long bu27034_scan_masks[] = {
 };
 
 /*
- * Available scales with gain 1x - 4096x, timings 55, 100, 200, 400 mS
+ * Available scales with gain 1x - 1024x, timings 55, 100, 200, 400 mS
  * Time impacts to gain: 1x, 2x, 4x, 8x.
  *
- * => Max total gain is HWGAIN * gain by integration time (8 * 4096) = 32768
+ * => Max total gain is HWGAIN * gain by integration time (8 * 1024) = 8192
+ * if 1x gain is scale 1, scale for 2x gain is 0.5, 4x => 0.25,
+ * ... 8192x => 0.0001220703125 => 122070.3125 nanos
  *
- * Using NANO precision for scale we must use scale 64x corresponding gain 1x
- * to avoid precision loss. (32x would result scale 976 562.5(nanos).
+ * Using NANO precision for scale, we must use scale 16x corresponding gain 1x
+ * to avoid precision loss. (8x would result scale 976 562.5(nanos).
  */
-#define BU27034_SCALE_1X	64
+#define BU27034_SCALE_1X	16
 
 /* See the data sheet for the "Gain Setting" table */
 #define BU27034_GSEL_1X		0x00 /* 00000 */
 #define BU27034_GSEL_4X		0x08 /* 01000 */
-#define BU27034_GSEL_16X	0x0a /* 01010 */
 #define BU27034_GSEL_32X	0x0b /* 01011 */
-#define BU27034_GSEL_64X	0x0c /* 01100 */
 #define BU27034_GSEL_256X	0x18 /* 11000 */
 #define BU27034_GSEL_512X	0x19 /* 11001 */
 #define BU27034_GSEL_1024X	0x1a /* 11010 */
-#define BU27034_GSEL_2048X	0x1b /* 11011 */
-#define BU27034_GSEL_4096X	0x1c /* 11100 */
 
 /* Available gain settings */
 static const struct iio_gain_sel_pair bu27034_gains[] = {
 	GAIN_SCALE_GAIN(1, BU27034_GSEL_1X),
 	GAIN_SCALE_GAIN(4, BU27034_GSEL_4X),
-	GAIN_SCALE_GAIN(16, BU27034_GSEL_16X),
 	GAIN_SCALE_GAIN(32, BU27034_GSEL_32X),
-	GAIN_SCALE_GAIN(64, BU27034_GSEL_64X),
 	GAIN_SCALE_GAIN(256, BU27034_GSEL_256X),
 	GAIN_SCALE_GAIN(512, BU27034_GSEL_512X),
 	GAIN_SCALE_GAIN(1024, BU27034_GSEL_1024X),
-	GAIN_SCALE_GAIN(2048, BU27034_GSEL_2048X),
-	GAIN_SCALE_GAIN(4096, BU27034_GSEL_4096X),
 };
 
 /*
- * The IC has 5 modes for sampling time. 5 mS mode is exceptional as it limits
- * the data collection to data0-channel only and cuts the supported range to
- * 10 bit. It is not supported by the driver.
- *
- * "normal" modes are 55, 100, 200 and 400 mS modes - which do have direct
- * multiplying impact to the register values (similar to gain).
+ * Measurement modes are 55, 100, 200 and 400 mS modes - which do have direct
+ * multiplying impact to the data register values (similar to gain).
  *
  * This means that if meas-mode is changed for example from 400 => 200,
  * the scale is doubled. Eg, time impact to total gain is x1, x2, x4, x8.
-- 
2.45.1


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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