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Mon, 05 May 2025 11:28:48 -0700 (PDT) From: David Lechner Date: Mon, 05 May 2025 13:28:40 -0500 Subject: [PATCH] iio: adc: ad7944: max high bits on direct read Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250505-iio-adc-ad7944-max-high-bits-on-direct-read-v1-1-b173facceefe@baylibre.com> X-B4-Tracking: v=1; b=H4sIAFcDGWgC/x2NQQqDMBBFryKz7kCaKGqvUrqImamZRZMyERHEu 3coj794m/9OaKzCDR7dCcq7NKnF5H7rIOVYVkYhc/DOD85AkYqRkm2c+x4/8cAsa8ZFtoa1IIl y2lA5Ei5hmPw0kwthBHv8Kr/l+Neer+v6AeJlOe19AAAA X-Change-ID: 20250505-iio-adc-ad7944-max-high-bits-on-direct-read-b358289d0337 To: Michael Hennerich , =?utf-8?q?Nuno_S=C3=A1?= , Jonathan Cameron Cc: Jonathan Cameron , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, David Lechner X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=1404; i=dlechner@baylibre.com; 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As we found recently, SPI controllers may not set unused bits to 0 when reading with bits_per_word !=3D {8,16,32}. The ad7944 uses bits_per_word of 14 and 18, so we need to mask the value to be sure we returning the correct value to userspace during a direct read. Fixes: d1efcf8871db ("iio: adc: ad7944: add driver for AD7944/AD7985/AD7986= ") Signed-off-by: David Lechner Reviewed-by: Nuno S=C3=A1 --- The sign_extend32() already takes care of signed reads in case that isn't obvious - it overwrites the unknown bits with the sign bit. --- drivers/iio/adc/ad7944.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c index 2f949fe5587318957f2e423029294ced0a6f803d..37a137bd83571b055e970a8cd48= 3d8726972d637 100644 --- a/drivers/iio/adc/ad7944.c +++ b/drivers/iio/adc/ad7944.c @@ -377,6 +377,8 @@ static int ad7944_single_conversion(struct ad7944_adc *= adc, =20 if (chan->scan_type.sign =3D=3D 's') *val =3D sign_extend32(*val, chan->scan_type.realbits - 1); + else + *val &=3D GENMASK(chan->scan_type.realbits - 1, 0); =20 return IIO_VAL_INT; } --- base-commit: b72f1157bfb9b92b0439e11469f7f94e47363460 change-id: 20250505-iio-adc-ad7944-max-high-bits-on-direct-read-b358289d0337 Best regards, --=20 David Lechner