[PATCH 04/13] HID: ft260: i2c: reduce driver module loading time

[Michael Zaidman]

The HWMON class I2C client drivers register the address range to scan
during the I2C master module probing. For example, the lm75 module
registers eight bus addresses scanned during the ft260 module loading.

In the case of ft260, the bus is scanned by ft260_i2c_read, but due to
an excessive read completion timeout, it took about 40 seconds for the
ft260 driver to scan the lm75 address range before exiting the probe
function.

Adjust the i2c_read timeout so it depends on the amount of data to
read, reducing the lm75 address range scan time to about 200ms.

The 25 ms per-report budget was checked on a UMFT260EV1A with a 24LC512
EEPROM by shrinking the timeout until reads began to fail: a 60-byte
read still completes at 9 ms and times out at 7 ms, against 5.4 ms of
wire time at 100 kHz, so the fixed USB, HID and scheduling overhead
costs a few milliseconds. At the chip's slowest 60 kHz clock that chunk
needs about 9 ms on the wire and the 180-byte chunk about 27 ms, so both
keep roughly a factor of two under the 25 ms and 75 ms limits and the
timeouts do not need retuning for slower bus clocks.

Signed-off-by: Michael Zaidman <michael.zaidman@xxxxxxxxx>
---
 drivers/hid/hid-ft260.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index cc3b8f5791de..4435a39fce23 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -56,6 +56,13 @@ MODULE_PARM_DESC(debug, "Toggle FT260 debugging messages");
  * read payload length to be 180 bytes.
  */
 #define FT260_RD_DATA_MAX (180)
+
+/* Time in ms to wait for a single report read data transfer completion */
+#define FT260_RD_ONE_REPORT_TO (25)
+
+/* Time in ms to wait for a multi-report read data transfer completion */
+#define FT260_RD_MULTI_REPORT_TO (FT260_RD_ONE_REPORT_TO * FT260_RD_DATA_MAX / 60)
+
 #define FT260_WR_I2C_DATA_MAX (60)
 #define FT260_WR_UART_DATA_MAX (62)
 #define FT260_GPIOCHIP "ft260_gpio"
@@ -713,7 +720,7 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 {
 	u16 rd_len;
 	u16 rd_data_max = 60;
-	int timeout, ret = 0;
+	int timeout, timeout_jiffies, ret = 0;
 	struct ft260_i2c_read_request_report rep;
 	struct hid_device *hdev = dev->hdev;
 	unsigned long irqflags;
@@ -732,10 +739,12 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 		flag = 0;	/* no fresh START - continue current transaction */
 	do {
 		if (len <= rd_data_max) {
+			timeout = FT260_RD_ONE_REPORT_TO;
 			rd_len = len;
 			if (want_stop)
 				flag |= FT260_FLAG_STOP;
 		} else {
+			timeout = FT260_RD_MULTI_REPORT_TO;
 			rd_len = rd_data_max;
 		}
 		rd_data_max = FT260_RD_DATA_MAX;
@@ -762,8 +771,8 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 			goto ft260_i2c_read_exit;
 		}
 
-		timeout = msecs_to_jiffies(5000);
-		if (!wait_for_completion_timeout(&dev->wait, timeout)) {
+		timeout_jiffies = msecs_to_jiffies(timeout);
+		if (!wait_for_completion_timeout(&dev->wait, timeout_jiffies)) {
 			ret = -ETIMEDOUT;
 			ft260_i2c_reset(hdev);
 			goto ft260_i2c_read_exit;
-- 
2.43.0