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From:   David Lechner <dlechner@baylibre.com>
To:     linux-iio@vger.kernel.org, linux-staging@lists.linux.dev
Cc:     David Lechner <dlechner@baylibre.com>,
        Jonathan Cameron <jic23@kernel.org>,
        Michael Hennerich <Michael.Hennerich@analog.com>,
        =?utf-8?q?Nuno_S=C3=A1?= <nuno.sa@analog.com>,
        Axel Haslam <ahaslam@baylibre.com>,
        Philip Molloy <pmolloy@baylibre.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v4 01/17] staging: iio: resolver: ad2s1210: do not use fault register for dummy read
Date:   Thu,  5 Oct 2023 19:50:18 -0500
Message-ID: <20231005-ad2s1210-mainline-v4-1-ec00746840fc@baylibre.com>
In-Reply-To: <20231005-ad2s1210-mainline-v4-0-ec00746840fc@baylibre.com>
References: <20231005-ad2s1210-mainline-v4-0-ec00746840fc@baylibre.com>
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When reading registers on the AD2S1210 chip, we have to supply a "dummy"
address for the second SPI tx byte so that we don't accidentally write
to a register. This register will be read and the value discarded on the
next regmap read or write call.

Reading the fault register has a side-effect of clearing the faults
so we should not use this register for the dummy read.

Signed-off-by: David Lechner <dlechner@baylibre.com>
---

v4 changes: New patch

(this probably should have been done before "staging: iio: resolver:
ad2s1210: use regmap for config registers" but was overlooked until now)

 drivers/staging/iio/resolver/ad2s1210.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
index 67d8af0dd7ae..8fbde9517fe9 100644
--- a/drivers/staging/iio/resolver/ad2s1210.c
+++ b/drivers/staging/iio/resolver/ad2s1210.c
@@ -166,9 +166,10 @@ static int ad2s1210_regmap_reg_read(void *context, unsigned int reg,
 	st->tx[0] = reg;
 	/*
 	 * Must be valid register address here otherwise this could write data.
-	 * It doesn't matter which one.
+	 * It doesn't matter which one as long as reading doesn't have side-
+	 * effects.
 	 */
-	st->tx[1] = AD2S1210_REG_FAULT;
+	st->tx[1] = AD2S1210_REG_CONTROL;
 
 	ret = spi_sync_transfer(st->sdev, xfers, ARRAY_SIZE(xfers));
 	if (ret < 0)

-- 
2.42.0