[PATCH v4 10/15] iio: adc: xilinx-xadc: Add clarifying comments

[Dileep Kumar Nagavarapu <dileepkumar.nagavarapu@amd.com>]

Add missing comments on struct mutex and spinlock_t in struct xadc
(per checkpatch.pl), and explain the non-obvious FIFO-drain loop and
Zynq alarm-bit reordering logic.

No functional change intended.

Co-developed-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
Signed-off-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
Signed-off-by: Dileep Kumar Nagavarapu <dileepkumar.nagavarapu@amd.com>
---
 drivers/iio/adc/xilinx-xadc-core.c | 9 +++++++++
 drivers/iio/adc/xilinx-xadc.h      | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
index 46b95883a250..47fa4d516611 100644
--- a/drivers/iio/adc/xilinx-xadc-core.c
+++ b/drivers/iio/adc/xilinx-xadc-core.c
@@ -133,6 +133,11 @@ static void xadc_zynq_drain_fifo(struct xadc *xadc)
 
 	xadc_read_reg(xadc, XADC_ZYNQ_REG_STATUS, &status);
 
+	/*
+	 * Reading XADC_ZYNQ_REG_DFIFO pops one entry from the data FIFO.
+	 * The loop therefore removes one pending entry per iteration and
+	 * terminates once the hardware reports the FIFO empty.
+	 */
 	while (!(status & XADC_ZYNQ_STATUS_DFIFOE)) {
 		xadc_read_reg(xadc, XADC_ZYNQ_REG_DFIFO, &tmp);
 		xadc_read_reg(xadc, XADC_ZYNQ_REG_STATUS, &status);
@@ -216,6 +221,10 @@ static int xadc_zynq_read_adc_reg(struct xadc *xadc, unsigned int reg, u16 *val)
 
 static unsigned int xadc_zynq_transform_alarm(unsigned int alarm)
 {
+	/*
+	 * Reorder the Zynq PS-XADC alarm bits defined in UG585 to match the common
+	 * XADC driver alarm layout.
+	 */
 	return ((alarm & 0x80) >> 4) | ((alarm & 0x78) << 1) | (alarm & 0x07);
 }
 
diff --git a/drivers/iio/adc/xilinx-xadc.h b/drivers/iio/adc/xilinx-xadc.h
index a659b7981b2f..cb48a5a38e8b 100644
--- a/drivers/iio/adc/xilinx-xadc.h
+++ b/drivers/iio/adc/xilinx-xadc.h
@@ -60,7 +60,9 @@ struct xadc {
 	unsigned int zynq_intmask;
 	struct delayed_work zynq_unmask_work;
 
+	/* Serializes register access and device configuration updates */
 	struct mutex mutex;
+	/* Protects interrupt state and FIFO operations */
 	spinlock_t lock;
 
 	struct completion completion;
-- 
2.34.1