patch "iio: ltc2497: Fix reading conversion results" added to char-misc-next

This is a note to let you know that I've just added the patch titled

iio: ltc2497: Fix reading conversion results

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From 7f4f1096d5921f5d90547596f9ce80e0b924f887 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <[email protected]>
Date: Mon, 15 Aug 2022 09:16:47 +0000
Subject: iio: ltc2497: Fix reading conversion results
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After the result of the previous conversion is read the chip automatically starts a new conversion and doesn't accept new i2c transfers until this conversion is completed which makes the function return failure.

So add an early return iff the programming of the new address isn't needed. Note this will not fix the problem in general, but all cases that are currently used. Once this changes we get the failure back, but this can be addressed when the need arises.

---
 drivers/iio/adc/ltc2497.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

index f7c786f37ceb..78b93c99cc47 100644
@@ -41,6 +41,19 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
 		}
 
 		*val = (be32_to_cpu(st->buf) >> 14) - (1 << 17);
+
+		/*
+		 * The part started a new conversion at the end of the above i2c
+		 * transfer, so if the address didn't change since the last call
+		 * everything is fine and we can return early.
+		 * If not (which should only happen when some sort of bulk
+		 * conversion is implemented) we have to program the new
+		 * address. Note that this probably fails as the conversion that
+		 * was triggered above is like not complete yet and the two
+		 * operations have to be done in a single transfer.
+		 */
+		if (ddata->addr_prev == address)
+			return 0;
 	}
 
 	ret = i2c_smbus_write_byte(st->client,

2.37.3