[PATCH 13/13] HID: ft260: i2c: abort in-flight transfers with STOP before reset

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

A transfer that ends without STOP leaves the FT260 I2C controller
with BUS_BUSY set. I2C reset (AN_394 section 4.4.15) restarts the
master but, with the driver still bound, status stays 0x60
(CTRL_IDLE | BUS_BUSY) even when SCL and SDA are pulled up. The
next START then fails with 0x72 (arbitration lost + error) and
further resets do not recover; only a USB replug did.

Add ft260_i2c_abort(): a STOP-only write (flag 0x04, zero payload)
then FT260_SET_I2C_RESET. Use it wherever the host tears down an
open transaction:

  - read wait timeout
  - read status check failure after the HID report arrived
  - write status poll failure after the report was sent
  - SMBus block read with an invalid count (count phase has no STOP)

Leave ft260_i2c_reset() alone for HID output failure (the request
may never have reached the controller), sysfs i2c_reset, and probe.

Tested on a UMFT260EV1A with a 24LC512 at 0x51. Five 1 ms read
timeouts each followed by STOP+reset left bus_status 0x20; raising
the timeout to 25 ms on the same loaded module then read 16 bytes
successfully.

This matters more with the 25/75 ms completion timeout from
"HID: ft260: i2c: reduce driver module loading time", which makes
read timeouts more likely than mainline's 5000 ms wait.

Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
---
 drivers/hid/hid-ft260.c | 43 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 36 insertions(+), 7 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 9ae688f6208f..a35a1af2d7e5 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -538,6 +538,33 @@ static int ft260_i2c_reset(struct hid_device *hdev)
 	return ret;
 }
 
+static int ft260_hid_output_report(struct hid_device *hdev, u8 *data,
+				   size_t len);
+
+/*
+ * STOP with no START and no payload. Used by ft260_i2c_abort() when
+ * tearing down an in-flight transfer: I2C reset alone can leave
+ * BUS_BUSY set even when SCL/SDA are idle, and the next START then
+ * fails with arbitration lost.
+ */
+static int ft260_i2c_stop(struct hid_device *hdev, u8 addr)
+{
+	u8 buf[4] = {
+		FT260_I2C_REPORT_MIN,
+		addr,
+		FT260_FLAG_STOP,
+		0,
+	};
+
+	return ft260_hid_output_report(hdev, buf, sizeof(buf));
+}
+
+static int ft260_i2c_abort(struct hid_device *hdev, u8 addr)
+{
+	ft260_i2c_stop(hdev, addr);
+	return ft260_i2c_reset(hdev);
+}
+
 static int ft260_xfer_status(struct ft260_device *dev, u8 bus_busy)
 {
 	struct hid_device *hdev = dev->hdev;
@@ -607,7 +634,8 @@ 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 bus_busy)
+						u8 *data, int len, u8 addr,
+						u8 bus_busy)
 {
 	int ret, usec, try = 100;
 	struct hid_device *hdev = dev->hdev;
@@ -636,7 +664,7 @@ static int ft260_hid_output_report_check_status(struct ft260_device *dev,
 	if (ret == 0)
 		return 0;
 
-	ft260_i2c_reset(hdev);
+	ft260_i2c_abort(hdev, addr);
 	return -EIO;
 }
 
@@ -675,7 +703,8 @@ 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, bus_busy);
+							   wr_len + 4, addr,
+							   bus_busy);
 		if (ret < 0) {
 			ft260_dbg("%s: failed with %d\n", __func__, ret);
 			return ret;
@@ -716,7 +745,7 @@ 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, addr,
 						   (flag & FT260_FLAG_STOP) ?
 						   FT260_I2C_STATUS_BUS_BUSY : 0);
 	if (ret < 0)
@@ -784,7 +813,7 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 		timeout_jiffies = msecs_to_jiffies(timeout);
 		if (!wait_for_completion_timeout(&dev->wait, timeout_jiffies)) {
 			ret = -ETIMEDOUT;
-			ft260_i2c_reset(hdev);
+			ft260_i2c_abort(hdev, addr);
 			goto ft260_i2c_read_exit;
 		}
 
@@ -798,7 +827,7 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 		ret = ft260_xfer_status(dev, bus_busy);
 		if (ret < 0) {
 			ret = -EIO;
-			ft260_i2c_reset(hdev);
+			ft260_i2c_abort(hdev, addr);
 			goto ft260_i2c_read_exit;
 		}
 
@@ -982,7 +1011,7 @@ static int ft260_smbus_xfer(struct i2c_adapter *adapter, u16 addr, u16 flags,
 				hid_warn(hdev,
 					 "smbus block read: invalid count %u from slave 0x%02x\n",
 					 count, addr);
-				ft260_i2c_reset(hdev);
+				ft260_i2c_abort(hdev, addr);
 				ret = -EPROTO;
 				goto smbus_exit;
 			}
-- 
2.43.0