From fda643a9530c86e503a90791392443cd47f3c997 Mon Sep 17 00:00:00 2001 From: Jonathan Cameron Date: Sun, 13 Apr 2025 11:34:29 +0100 Subject: [PATCH] iio: dummy: Use a fixed structure to build up scan to push to buffers. It has long been discouraged for drivers to make use of iio_dev->scan_bytes directly as that is an implementation detail of the core. As such our example driver should definitely not be doing so. In order to illustrate the more complex case, where a DMA safe buffer is needed, continue to kzalloc() the storage (but with a structure definition to provide an explicit data layout). Also add comments on when a DMA safe buffer is necessary and the two common ways of obtaining one. Whilst we have a mixture of signed and unsigned channels, the unsigned channels have ranges that can be stored in a signed value - hence use signed storage for all channels, simplifying the structure definition. Reviewed-by: David Lechner Link: https://patch.msgid.link/20250413103443.2420727-7-jic23@kernel.org Signed-off-by: Jonathan Cameron --- drivers/iio/dummy/iio_simple_dummy_buffer.c | 25 +++++++++++++++------ 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/drivers/iio/dummy/iio_simple_dummy_buffer.c b/drivers/iio/dummy/iio_simple_dummy_buffer.c index 288880346707..d0a7343e1b35 100644 --- a/drivers/iio/dummy/iio_simple_dummy_buffer.c +++ b/drivers/iio/dummy/iio_simple_dummy_buffer.c @@ -31,6 +31,11 @@ static const s16 fakedata[] = { [DUMMY_INDEX_ACCELX] = 344, }; +struct dummy_scan { + s16 data[ARRAY_SIZE(fakedata)]; + aligned_s64 timestamp; +}; + /** * iio_simple_dummy_trigger_h() - the trigger handler function * @irq: the interrupt number @@ -45,11 +50,18 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq, void *p) { struct iio_poll_func *pf = p; struct iio_dev *indio_dev = pf->indio_dev; + struct dummy_scan *scan; int i = 0, j; - u16 *data; - data = kzalloc(indio_dev->scan_bytes, GFP_KERNEL); - if (!data) + /* + * Note that some buses such as SPI require DMA safe buffers which + * cannot be on the stack. Two easy ways to do this: + * - Local kzalloc (as done here) + * - A buffer at the end of the structure accessed via iio_priv() + * that is marked __aligned(IIO_DMA_MINALIGN). + */ + scan = kzalloc(sizeof(*scan), GFP_KERNEL); + if (!scan) goto done; /* @@ -69,13 +81,12 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq, void *p) * constant table fakedata. */ iio_for_each_active_channel(indio_dev, j) - data[i++] = fakedata[j]; + scan->data[i++] = fakedata[j]; - iio_push_to_buffers_with_timestamp(indio_dev, data, + iio_push_to_buffers_with_timestamp(indio_dev, scan, iio_get_time_ns(indio_dev)); - kfree(data); - + kfree(scan); done: /* * Tell the core we are done with this trigger and ready for the -- 2.20.1