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From: Adam Michaelis <adam.michaelis@rockwellcollins.com>
To: linux-iio@vger.kernel.org
Cc: lars@metafoo.de, michael.hennerich@analog.com, jic23@kernel.org,
	knaack.h@gmx.de, pmeerw@pmeerw.net, robh+dt@kernel.org,
	mark.rutland@arm.com, charles-antoine.couret@essensium.com,
	devicetree@vger.kernel.org, brandon.maier@rockwellcollins.com,
	clayton.shotwell@rockwellcollins.com,
	Adam Michaelis <adam.michaelis@rockwellcollins.com>
Subject: [PATCH v3 1/5] iio: ad7949: Fix dummy read cycle placement
Date: Mon, 13 May 2019 09:53:01 -0500
Message-ID: <1557759185-167857-1-git-send-email-adam.michaelis@rockwellcollins.com> (raw)

The AD7949 requires two conversion cycles following the first
configuration change, and one extra cycle following any other
configuration change (including changing the analog channel being
sampled). Therefore, adding a dummy read cycle when config is changed
and removing the extra cycle at initial configuration (the first dummy
cycle is now performed as part of applying the configuration change).

Signed-off-by: Adam Michaelis <adam.michaelis@rockwellcollins.com>
---
	V2:
	- Add some defines to reduce use of magic numbers.
	V3:
	- Switch back to using a u32 data buffer.
	- Add-back the second dummy cycle on initialization.
	- Move to first patch in series.
---
 drivers/iio/adc/ad7949.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
index ac0ffff6c5ae..c7fe27aa2519 100644
--- a/drivers/iio/adc/ad7949.c
+++ b/drivers/iio/adc/ad7949.c
@@ -100,6 +100,23 @@ static int ad7949_spi_write_cfg(struct ad7949_adc_chip *ad7949_adc, u16 val,
 	 * send a new command to the device
 	 */
 	udelay(2);
+
+	/*
+	 * Perform extra read cycle to allow configuration, acquisition,
+	 * and conversion sequences to complete for new configuration.
+	 */
+	ad7949_adc->buffer = 0;
+
+	spi_message_init_with_transfers(&msg, tx, 1);
+
+	ret = spi_sync(ad7949_adc->spi, &msg);
+
+	/*
+	 * This delay is to avoid a new request before the required time
+	 * to send a new command to the device.
+	 */
+	udelay(2);
+
 	return ret;
 }
 
@@ -229,11 +246,10 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 	ret = ad7949_spi_write_cfg(ad7949_adc, 0x3C79, AD7949_MASK_TOTAL);
 
 	/*
-	 * Do two dummy conversions to apply the first configuration setting.
+	 * Do a dummy conversion to apply the first configuration setting.
 	 * Required only after the start up of the device.
 	 */
 	ad7949_spi_read_channel(ad7949_adc, &val, ad7949_adc->current_channel);
-	ad7949_spi_read_channel(ad7949_adc, &val, ad7949_adc->current_channel);
 
 	return ret;
 }
-- 
1.9.1


             reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-13 14:53 Adam Michaelis [this message]
2019-05-13 14:53 ` [PATCH v3 2/5] iio: ad7949: Support internal Vref Adam Michaelis
2019-05-18  9:07   ` Jonathan Cameron
2019-05-23 12:12   ` Alexandru Ardelean
2019-05-23 12:51     ` Ardelean, Alexandru
2019-05-13 14:53 ` [PATCH v3 3/5] dt-bindings: iio: ad7949: Add adi,reference-select Adam Michaelis
2019-05-14 18:23   ` Rob Herring
2019-05-18  9:07     ` Jonathan Cameron
2019-05-23 12:16       ` Alexandru Ardelean
2019-05-13 14:53 ` [PATCH v3 4/5] iio: ad7949: Fix SPI interfacing for 14-bit messages Adam Michaelis
2019-05-18  9:10   ` Jonathan Cameron
2019-05-23 12:39     ` Alexandru Ardelean
2019-05-13 14:53 ` [PATCH v3 5/5] iio: ad7949: Remove logic for config readback Adam Michaelis
2019-05-18  9:19   ` Jonathan Cameron
2019-05-23 11:47 ` [PATCH v3 1/5] iio: ad7949: Fix dummy read cycle placement Alexandru Ardelean
2019-05-24 11:49   ` Couret Charles-Antoine

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