[PATCH v2 10/15] HID: ft260: i2c: fix large write transaction failure

[Michael Zaidman <michael.zaidman@gmail.com>]

Fixes a regression from commit 5afac727defa ("HID: ft260: missed NACK
from busy device"), which waited for bus-idle after every HID write
report except when the report flag was exactly FT260_FLAG_START.

Multi-report I2C writes keep the bus busy between chunks for atomicity.
Treating those middle reports like a final STOP caused ft260_xfer_status()
to spin on -EAGAIN after the second HID report and fail large writes.
Write-then-read combined transfers still worked.

Pass the bus-busy check policy from the caller: ft260_i2c_write() and
ft260_smbus_write() wait for idle only when the report they send carries
STOP; intermediate chunks and the command phase of a combined transfer
do not.

The SMBus side matters for register reads. The command phase is written
with FT260_FLAG_START and no STOP, because a repeated START read follows
and the controller deliberately keeps the bus busy to keep the
transaction atomic. Checking the busy bit there makes
ft260_xfer_status() return -EAGAIN on every retry and the command write
fail with -EIO, which breaks probing of clients that read registers:

  ads1x19 6-0040: Failed to read config register: -5
  leds-pca963x: probe of 6-0008 failed with error -5

Fixes: 5afac727defa ("HID: ft260: missed NACK from busy device")
Reported-by: Chris Keeser <chriskeeser@meta.com>
Closes: https://github.com/MichaelZaidman/hid-ft260/issues/35
Tested-by: Chris Keeser <chriskeeser@meta.com>
Reported-by: Bruno Giacomazzi <brunoceg1@gmail.com>
Closes: https://github.com/MichaelZaidman/hid-ft260/issues/42
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
---
 drivers/hid/hid-ft260.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index dca0250f2c25..65835e13fa2a 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -576,9 +576,14 @@ static int ft260_xfer_status(struct ft260_device *dev, u8 bus_busy)
 	}
 
 	dev->clock = le16_to_cpu(report.clock);
-	ft260_dbg("bus_status %#02x, clock %u\n", report.bus_status,
-		  dev->clock);
+	ft260_dbg("bus_status %#02x, clock %u, bus_busy %#02x\n",
+		  report.bus_status, dev->clock, bus_busy);
 
+	/*
+	 * Do not check the busy bit for combined transactions
+	 * since the controller keeps the bus busy between writing
+	 * and reading IOs to ensure an atomic operation.
+	 */
 	if (report.bus_status & (FT260_I2C_STATUS_CTRL_BUSY | bus_busy))
 		return -EAGAIN;
 
@@ -612,13 +617,10 @@ static int ft260_hid_output_report(struct hid_device *hdev, u8 *data,
 }
 
 static int ft260_hid_output_report_check_status(struct ft260_device *dev,
-						u8 *data, int len)
+						u8 *data, int len, u8 bus_busy)
 {
-	u8 bus_busy;
 	int ret, usec, try = 100;
 	struct hid_device *hdev = dev->hdev;
-	struct ft260_i2c_write_request_report *rep =
-		(struct ft260_i2c_write_request_report *)data;
 
 	ret = ft260_hid_output_report(hdev, data, len);
 	if (ret < 0) {
@@ -635,16 +637,6 @@ static int ft260_hid_output_report_check_status(struct ft260_device *dev,
 		ft260_dbg("wait %d usec, len %d\n", usec, len);
 	}
 
-	/*
-	 * Do not check the busy bit for combined transactions
-	 * since the controller keeps the bus busy between writing
-	 * and reading IOs to ensure an atomic operation.
-	 */
-	if (rep->flag == FT260_FLAG_START)
-		bus_busy = 0;
-	else
-		bus_busy = FT260_I2C_STATUS_BUS_BUSY;
-
 	do {
 		ret = ft260_xfer_status(dev, bus_busy);
 		if (ret != -EAGAIN)
@@ -661,6 +653,7 @@ static int ft260_hid_output_report_check_status(struct ft260_device *dev,
 static int ft260_i2c_write(struct ft260_device *dev, u8 addr, u8 *data,
 			   int len, u8 flag)
 {
+	u8 bus_busy = 0;
 	int ret, wr_len, idx = 0;
 	struct ft260_i2c_write_request_report *rep =
 		(struct ft260_i2c_write_request_report *)dev->i2c_wr_buf;
@@ -673,8 +666,10 @@ static int ft260_i2c_write(struct ft260_device *dev, u8 addr, u8 *data,
 	do {
 		if (len <= FT260_WR_I2C_DATA_MAX) {
 			wr_len = len;
-			if (flag == FT260_FLAG_START_STOP)
+			if (flag == FT260_FLAG_START_STOP) {
 				rep->flag |= FT260_FLAG_STOP;
+				bus_busy = FT260_I2C_STATUS_BUS_BUSY;
+			}
 		} else {
 			wr_len = FT260_WR_I2C_DATA_MAX;
 		}
@@ -690,7 +685,7 @@ static int ft260_i2c_write(struct ft260_device *dev, u8 addr, u8 *data,
 			  rep->flag, data[0]);
 
 		ret = ft260_hid_output_report_check_status(dev, (u8 *)rep,
-							   wr_len + 4);
+							   wr_len + 4, bus_busy);
 		if (ret < 0) {
 			ft260_dbg("failed with %d\n", ret);
 			return ret;
@@ -731,7 +726,9 @@ static int ft260_smbus_write(struct ft260_device *dev, u8 addr, u8 cmd,
 	ft260_dbg("rep %#02x addr %#02x cmd %#02x datlen %d replen %d\n",
 		  rep->report, addr, cmd, rep->length, len);
 
-	ret = ft260_hid_output_report_check_status(dev, (u8 *)rep, len);
+	ret = ft260_hid_output_report_check_status(dev, (u8 *)rep, len,
+						   (flag & FT260_FLAG_STOP) ?
+						   FT260_I2C_STATUS_BUS_BUSY : 0);
 	if (ret < 0)
 		ft260_dbg("failed with %d\n", ret);
 
-- 
2.43.0