kernel_optimize_test/drivers/i2c
Russell King 4d6d5f1d08 i2c: designware: fix rx fifo depth tracking
When loading the TX fifo to receive bytes on the I2C bus, we incorrectly
count the number of bytes:

	rx_limit = dev->rx_fifo_depth - dw_readl(dev, DW_IC_RXFLR);

	while (buf_len > 0 && tx_limit > 0 && rx_limit > 0) {
		if (rx_limit - dev->rx_outstanding <= 0)
			break;
		rx_limit--;
		dev->rx_outstanding++;
	}

DW_IC_RXFLR indicates how many bytes are available to be read in the
FIFO, dev->rx_fifo_depth is the FIFO size, and dev->rx_outstanding is
the number of bytes that we've requested to be read so far, but which
have not been read.

Firstly, increasing dev->rx_outstanding and decreasing rx_limit and then
comparing them results in each byte consuming "two" bytes in this
tracking, so this is obviously wrong.

Secondly, the number of bytes that _could_ be received into the FIFO at
any time is the number of bytes we have so far requested but not yet
read from the FIFO - in other words dev->rx_outstanding.

So, in order to request enough bytes to fill the RX FIFO, we need to
request dev->rx_fifo_depth - dev->rx_outstanding bytes.

Modifying the code thusly results in us reaching the maximum number of
bytes outstanding each time we queue more "receive" operations, provided
the transfer allows that to happen.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
2016-11-24 16:18:15 +01:00
..
algos i2c: algo-bit: declare i2c_bit_quirk_no_clk_stretch as static 2016-05-11 17:16:30 +02:00
busses i2c: designware: fix rx fifo depth tracking 2016-11-24 16:18:15 +01:00
muxes i2c: i2c-mux-pca954x: fix deselect enabling for device-tree 2016-11-19 21:49:29 +01:00
i2c-boardinfo.c i2c: remove __init from i2c_register_board_info() 2016-06-19 14:13:50 +02:00
i2c-core.c i2c: core: fix NULL pointer dereference under race condition 2016-11-04 20:36:58 +01:00
i2c-core.h i2c: remove FSF address 2014-11-07 18:35:33 +01:00
i2c-dev.c i2c-dev: don't get i2c adapter via i2c_dev 2016-07-08 10:29:31 +09:00
i2c-mux.c i2c: move locking operations to their own struct 2016-08-30 22:56:14 +02:00
i2c-slave-eeprom.c i2c: Drop owner assignment from i2c_driver 2015-08-10 08:37:35 +02:00
i2c-smbus.c i2c: i2c-smbus: fix i2c_handle_smbus_host_notify documentation 2016-07-18 20:09:54 +02:00
i2c-stub.c i2c: i2c-stub: sort includes 2016-02-20 23:33:39 +01:00
Kconfig i2c: mux: fix up dependencies 2016-11-14 18:23:30 +01:00
Makefile i2c: slave-eeprom: add eeprom simulator driver 2014-12-11 22:25:54 +01:00