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Thu, 27 Mar 2025 17:25:34 -0400 From: Marcelo Schmitt To: , , CC: , , , , , Subject: [PATCH v4 4/4] Documentation: iio: ad4000: Describe offload support Date: Thu, 27 Mar 2025 18:25:29 -0300 Message-ID: X-Mailer: git-send-email 2.39.2 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ADIRuleOP-NewSCL: Rule Triggered X-Authority-Analysis: v=2.4 cv=AdmxH2XG c=1 sm=1 tr=0 ts=67e5c25c cx=c_pps a=3WNzaoukacrqR9RwcOSAdA==:117 a=3WNzaoukacrqR9RwcOSAdA==:17 a=Vs1iUdzkB0EA:10 a=wI1k2SEZAAAA:8 a=IpJZQVW2AAAA:8 a=gAnH3GRIAAAA:8 a=k5wdjJE9De7JZY4JY-8A:9 a=6HWbV-4b7c7AdzY24d_u:22 a=IawgGOuG5U0WyFbmm1f5:22 X-Proofpoint-GUID: Ho3VjS0B-R19RczkJ6-dNP3TTD7dEw9p X-Proofpoint-ORIG-GUID: Ho3VjS0B-R19RczkJ6-dNP3TTD7dEw9p X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1095,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-27_04,2025-03-27_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 bulkscore=0 mlxlogscore=999 impostorscore=0 clxscore=1015 spamscore=0 malwarescore=0 mlxscore=0 suspectscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2502280000 definitions=main-2503270144 Content-Type: text/plain; charset="utf-8" When SPI offloading is supported, the IIO device provides different sysfs interfaces to allow using the adjusting the sample rate. Document SPI offload support for AD4000 and similar devices. Reviewed-by: David Lechner Signed-off-by: Marcelo Schmitt --- Documentation/iio/ad4000.rst | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/Documentation/iio/ad4000.rst b/Documentation/iio/ad4000.rst index 468d30dc9214..c1d04d3436d2 100644 --- a/Documentation/iio/ad4000.rst +++ b/Documentation/iio/ad4000.rst @@ -191,3 +191,30 @@ Typical voltage channel attributes of a differential A= D4000 series device: +-------------------------------------------+-----------------------------= -------------+ | ``in_voltage0-voltage1_scale_available`` | Toggles input span compressi= on | +-------------------------------------------+-----------------------------= -------------+ + +SPI offload support +------------------- + +To be able to achieve the maximum sample rate, the driver can be used with= SPI +offload engines such as the one usually present in `AXI SPI Engine`_, to p= rovide +SPI offload support. + +.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/pulsar_= adc/index.html + +To keep up with SPI offloading transfer speeds, the ADC must be connected = either +in 3-wire turbo mode or in 3-wire without busy indicator mode and have SPI +controller CS line connected to the CNV pin. + +When set for SPI offload support, the IIO device will provide different +interfaces. + +* Either ``in_voltage0_sampling_frequency`` or + ``in_voltage0-voltage1_sampling_frequency`` file is provided to allow se= tting + the sample rate. +* IIO trigger device is not provided (no ``trigger`` directory). +* ``timestamp`` channel is not provided. + +Also, because the ADC output has a one sample latency (delay) when the dev= ice is +wired in "3-wire" mode and only one transfer per sample is done when using= SPI +offloading, the first data sample in the buffer is not valid because it co= ntains +the output of an earlier conversion result. --=20 2.47.2