iio: buffer: Add industrialio-buffer-dmaengine-filtered

This is a hack to discard ADAQ4216 second channel data.

The ad4630_fmc HDL project was designed for ADCs with two channels and
always streams two data channels to DMA (even when the ADC has only one
physical channel). Though, if the ADC has only one physical channel, the
data that would come from the second ADC channel comes in as noise and has
to be discarded. Because of that, only half of data collected by DMA blocks
shall be passed to IIO buffers when using single-channel ADCs such as
ADAQ4216.

Because only half of the data pushed to DMA is used, the filtered dmaengine
buffer variant allocates blocks that are two times the usual size so the
IIO buffer can still be filled with the data from one DMA block. Otherwise,
a data glitch occurs right in the middle of the IIO buffer.

Add a separate dmaengine buffer variant for filtering data from ADAQ4216
and similar single-channel ADCs supported by the ad4630.c driver.

Signed-off-by: Marcelo Schmitt <[email protected]>

Author: machschmitt

drivers/iio/buffer/Kconfig

@@ -30,6 +30,19 @@ config IIO_BUFFER_DMAENGINE
 
 	  Should be selected by drivers that want to use this functionality.
 
+config IIO_BUFFER_DMAENGINE_FILTERED
+	tristate "Industrial I/O DMA buffer integration with DMAEngine that filters data"
+	select IIO_BUFFER_DMA
+	select IIO_BUFFER_DMAENGINE
+	help
+	  Provides a bonding of the generic IIO DMA buffer infrastructure with the
+	  DMAEngine framework. This can be used by converter drivers with a DMA port
+	  connected to an external DMA controller which is supported by the
+	  DMAEngine framework.
+
+	  Should NOT be selected by anything, unless using ADAQ4216 or similar
+	  single-channel ADCs supported by the ad4630.c driver.
+
 config IIO_DMA_BUF_MMAP_LEGACY
 	bool "Enables I/O DMA buffer legacy MMAP support"
 	depends on IIO_BUFFER_DMAENGINE

drivers/iio/buffer/Makefile

@@ -7,6 +7,7 @@
 obj-$(CONFIG_IIO_BUFFER_CB) += industrialio-buffer-cb.o
 obj-$(CONFIG_IIO_BUFFER_DMA) += industrialio-buffer-dma.o
 obj-$(CONFIG_IIO_BUFFER_DMAENGINE) += industrialio-buffer-dmaengine.o
+obj-$(CONFIG_IIO_BUFFER_DMAENGINE_FILTERED) += industrialio-buffer-dmaengine-filtered.o
 obj-$(CONFIG_IIO_BUFFER_HW_CONSUMER) += industrialio-hw-consumer.o
 obj-$(CONFIG_IIO_TRIGGERED_BUFFER) += industrialio-triggered-buffer.o
 obj-$(CONFIG_IIO_KFIFO_BUF) += kfifo_buf.o