patch "iio: adc: xilinx-ams: Fix single channel switching sequence" added to char-misc-next

patch "iio: adc: xilinx-ams: Fix single channel switching sequence" added to char-misc-next

[gregkh]

This is a note to let you know that I've just added the patch titled

    iio: adc: xilinx-ams: Fix single channel switching sequence

to my char-misc git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


From 0bf126163c3e7e6d722622073046aed567a5551e Mon Sep 17 00:00:00 2001
From: Robert Hancock <robert.hancock@calian.com>
Date: Thu, 27 Jan 2022 11:34:50 -0600
Subject: iio: adc: xilinx-ams: Fix single channel switching sequence

Some of the AMS channels need to be read by switching into single-channel
mode from the normal polling sequence. There was a logic issue in this
switching code that could cause the first read of these channels to read
back as zero.

It appears that the sequencer should be set back to default mode before
changing the channel selection, and the channel should be set before
switching the sequencer back into single-channel mode.

Also, write 1 to the EOC bit in the status register to clear it before
waiting for it to become set, so that we actually wait for a new
conversion to complete, and don't proceed based on a previous conversion
completing.

Fixes: d5c70627a794 ("iio: adc: Add Xilinx AMS driver")
Signed-off-by: Robert Hancock <robert.hancock@calian.com>
Acked-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20220127173450.3684318-5-robert.hancock@calian.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---
 drivers/iio/adc/xilinx-ams.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/xilinx-ams.c b/drivers/iio/adc/xilinx-ams.c
index 0c491667c464..a55396c1f8b2 100644
--- a/drivers/iio/adc/xilinx-ams.c
+++ b/drivers/iio/adc/xilinx-ams.c
@@ -531,14 +531,18 @@ static int ams_enable_single_channel(struct ams *ams, unsigned int offset)
 		return -EINVAL;
 	}
 
-	/* set single channel, sequencer off mode */
+	/* put sysmon in a soft reset to change the sequence */
 	ams_ps_update_reg(ams, AMS_REG_CONFIG1, AMS_CONF1_SEQ_MASK,
-			  AMS_CONF1_SEQ_SINGLE_CHANNEL);
+			  AMS_CONF1_SEQ_DEFAULT);
 
 	/* write the channel number */
 	ams_ps_update_reg(ams, AMS_REG_CONFIG0, AMS_CONF0_CHANNEL_NUM_MASK,
 			  channel_num);
 
+	/* set single channel, sequencer off mode */
+	ams_ps_update_reg(ams, AMS_REG_CONFIG1, AMS_CONF1_SEQ_MASK,
+			  AMS_CONF1_SEQ_SINGLE_CHANNEL);
+
 	return 0;
 }
 
@@ -552,6 +556,8 @@ static int ams_read_vcc_reg(struct ams *ams, unsigned int offset, u32 *data)
 	if (ret)
 		return ret;
 
+	/* clear end-of-conversion flag, wait for next conversion to complete */
+	writel(expect, ams->base + AMS_ISR_1);
 	ret = readl_poll_timeout(ams->base + AMS_ISR_1, reg, (reg & expect),
 				 AMS_INIT_POLL_TIME_US, AMS_INIT_TIMEOUT_US);
 	if (ret)
-- 
2.35.1