[PATCH v4 11/15] iio: adc: xilinx-xadc: Refine Zynq read/write error handling on timeout/interrupt

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

Refine the error codes returned from the wait, the same way in both
xadc_zynq_write_adc_reg() and xadc_zynq_read_adc_reg(): a timeout
(ret == 0) now returns -ETIMEDOUT instead of the previous -EIO,
giving a more precise errno for this condition. An interrupted wait
(ret < 0) now propagates that error to the caller instead of being
silently treated as success.

xadc_zynq_write_adc_reg() waits on xadc->completion after issuing the
Zynq DRP write command, then drains the response word from
XADC_ZYNQ_REG_DFIFO. The DFIFO read already ran unconditionally after
the wait, regardless of outcome.

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 | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
index 47fa4d516611..92cd38cd1834 100644
--- a/drivers/iio/adc/xilinx-xadc-core.c
+++ b/drivers/iio/adc/xilinx-xadc-core.c
@@ -172,14 +172,16 @@ static int xadc_zynq_write_adc_reg(struct xadc *xadc, unsigned int reg, u16 val)
 	}
 
 	ret = wait_for_completion_interruptible_timeout(&xadc->completion, HZ);
-	if (ret == 0)
-		ret = -EIO;
-	else
-		ret = 0;
 
 	xadc_read_reg(xadc, XADC_ZYNQ_REG_DFIFO, &tmp);
 
-	return ret;
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	if (ret < 0)
+		return ret;
+
+	return 0;
 }
 
 static int xadc_zynq_read_adc_reg(struct xadc *xadc, unsigned int reg, u16 *val)
@@ -207,7 +209,8 @@ static int xadc_zynq_read_adc_reg(struct xadc *xadc, unsigned int reg, u16 *val)
 
 	ret = wait_for_completion_interruptible_timeout(&xadc->completion, HZ);
 	if (ret == 0)
-		ret = -EIO;
+		return -ETIMEDOUT;
+
 	if (ret < 0)
 		return ret;
 
-- 
2.34.1