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([2600:8803:e7e4:500:a950:74e5:81f2:8c89]) by smtp.gmail.com with ESMTPSA id 006d021491bc7-6a36a3b0d60sm8823630eaf.0.2026.07.11.08.44.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 11 Jul 2026 08:44:36 -0700 (PDT) Message-ID: Date: Sat, 11 Jul 2026 10:44:35 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 3/4] iio: adc: ltc2378: Enable high-speed data capture To: Marcelo Schmitt , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jic23@kernel.org, nuno.sa@analog.com, Michael.Hennerich@analog.com, andy@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, julianbraha@gmail.com, marcelo.schmitt1@gmail.com References: <4d4b5cac52b6f4a341d97bd41562a451e8e757f7.1783629101.git.marcelo.schmitt@analog.com> Content-Language: en-US From: David Lechner In-Reply-To: <4d4b5cac52b6f4a341d97bd41562a451e8e757f7.1783629101.git.marcelo.schmitt@analog.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/9/26 3:50 PM, Marcelo Schmitt wrote: > Make use of SPI transfer offloading to speed up data capture, enabling data > acquisition at faster sample rates (up to 2 MSPS). > ... > +static int ltc2378_prepare_offload_message(struct device *dev, > + struct ltc2378_state *st) > +{ > + unsigned int resolution = st->info->offload_chan.scan_type.realbits; > + > + st->offload_xfer.bits_per_word = resolution; > + st->offload_xfer.len = spi_bpw_to_bytes(resolution); > + st->offload_xfer.offload_flags = SPI_OFFLOAD_XFER_RX_STREAM; > + > + /* Initialize message with offload */ > + spi_message_init_with_transfers(&st->offload_msg, &st->offload_xfer, 1); > + st->offload_msg.offload = st->offload; > + > + return devm_spi_optimize_message(dev, st->spi, &st->offload_msg); > +} Would be more logical to move this function after buffer stuff. > + > +static int ltc2378_offload_buffer_postenable(struct iio_dev *indio_dev) > +{ > + struct ltc2378_state *st = iio_priv(indio_dev); > + int ret; > + > + ret = pwm_set_waveform_might_sleep(st->cnv_trigger, &st->cnv_wf, true); > + if (ret) > + return ret; > + > + ret = spi_offload_trigger_enable(st->offload, st->offload_trigger, > + &st->offload_trigger_config); > + if (ret) > + goto out_pwm_disable; > + > + return 0; > + > +out_pwm_disable: > + pwm_disable(st->cnv_trigger); > + return ret; > +} > + > +static int ltc2378_offload_buffer_predisable(struct iio_dev *indio_dev) > +{ > + struct ltc2378_state *st = iio_priv(indio_dev); > + > + spi_offload_trigger_disable(st->offload, st->offload_trigger); > + pwm_disable(st->cnv_trigger); > + > + return 0; > +} > + > +static const struct iio_buffer_setup_ops ltc2378_offload_buffer_ops = { > + .postenable = <c2378_offload_buffer_postenable, > + .predisable = <c2378_offload_buffer_predisable, > +}; > + ... to here or even below somewhere. > +static int ltc2378_spi_offload_setup(struct iio_dev *indio_dev, > + struct ltc2378_state *st) > +{ > + struct device *dev = &st->spi->dev; > + struct dma_chan *rx_dma; > + > + indio_dev->setup_ops = <c2378_offload_buffer_ops; > + > + st->offload_trigger = devm_spi_offload_trigger_get(dev, st->offload, > + SPI_OFFLOAD_TRIGGER_PERIODIC); > + if (IS_ERR(st->offload_trigger)) > + return dev_err_probe(dev, PTR_ERR(st->offload_trigger), > + "failed to get offload trigger\n"); > + > + st->offload_trigger_config.type = SPI_OFFLOAD_TRIGGER_PERIODIC; > + > + rx_dma = devm_spi_offload_rx_stream_request_dma_chan(dev, st->offload); > + if (IS_ERR(rx_dma)) > + return dev_err_probe(dev, PTR_ERR(rx_dma), "failed to get offload RX DMA\n"); > + > + return devm_iio_dmaengine_buffer_setup_with_handle(dev, indio_dev, rx_dma, > + IIO_BUFFER_DIRECTION_IN); > +} > + ... > @@ -340,8 +672,53 @@ static int ltc2378_probe(struct spi_device *spi) > return dev_err_probe(dev, PTR_ERR(st->cnv_gpio), > "failed to get CNV GPIO"); > > - indio_dev->channels = &st->info->chan; > - indio_dev->num_channels = 1; > + st->offload = devm_spi_offload_get(dev, spi, <c2378_offload_config); > + ret = PTR_ERR_OR_ZERO(st->offload); > + /* Fall back to low speed usage when no SPI offload is available. */ > + if (ret == -ENODEV) { > + indio_dev->info = <c2378_iio_info; > + indio_dev->channels = &st->info->chan; > + indio_dev->num_channels = 1; > + } else if (ret) { > + return dev_err_probe(dev, ret, "failed to get offload\n"); > + } else { > + indio_dev->info = <c2378_offload_iio_info; > + indio_dev->channels = &st->info->offload_chan; > + indio_dev->num_channels = 1; > + ret = ltc2378_spi_offload_setup(indio_dev, st); > + if (ret) > + return dev_err_probe(dev, ret, > + "failed to setup SPI offload\n"); > + > + ret = ltc2378_pwm_get(st); > + if (ret) > + return dev_err_probe(dev, ret, "failed to get PWM\n"); > + > + st->sample_freq_range[0] = 1; /* min */ > + st->sample_freq_range[1] = 1; /* step */ > + st->sample_freq_range[2] = st->info->max_sample_rate_Hz; /* max */ > + > + /* > + * Start with a slower sampling rate so there is some room for > + * adjusting the sample averaging and the sampling frequency > + * without hitting the maximum conversion rate. > + */ > + ret = ltc2378_update_conversion_rate(st, st->info->max_sample_rate_Hz >> 4); > + if (ret) > + return dev_err_probe(dev, ret, > + "failed to set offload samp freq\n"); > + > + ret = ltc2378_prepare_offload_message(&spi->dev, st); > + if (ret) > + return dev_err_probe(dev, ret, "failed to optimize SPI message\n"); > + > + /* > + * Set single-read transfer bits_per_word so the SPI subsystem > + * rearanges data to CPU endianness, enabling us to reuse s/rearanges/rearranges/ > + * offload_chan specifications for single-shot reads. > + */ > + st->xfer.bits_per_word = st->info->offload_chan.scan_type.realbits; > + } > > st->xfer.rx_buf = &st->scan.data; > st->xfer.len = spi_bpw_to_bytes(indio_dev->channels[0].scan_type.realbits); > @@ -412,3 +789,4 @@ module_spi_driver(ltc2378_driver); > MODULE_AUTHOR("Marcelo Schmitt "); > MODULE_DESCRIPTION("Analog Devices LTC2378 ADC series driver"); > MODULE_LICENSE("GPL"); > +MODULE_IMPORT_NS("IIO_DMAENGINE_BUFFER");