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i2c: designware: size the RX FIFO threshold to the queued transfer

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i2c_dw_xfer_msg() leaves DW_IC_RX_TL at the 0 that i2c_dw_configure_mode()
writes, so the controller raises RX_FULL once per received byte. Program
RX_TL from the reads already queued, capped at half the FIFO until the last
message is queued, so there is room for the rest.

On an Arrow Lake-H LPSS core with rx_fifo_depth 32, a 22-byte HID input
report costs 2.00 interrupts instead of 21.43, and a 452-byte descriptor
0.14 interrupts per byte instead of 1.64. Polling the touchpad with
HIDIOCGINPUT at 142 Hz draws 1.58 W less platform power (psys, 32 paired
runs).

Assisted-by: LLM
Signed-off-by: Navon John Lukose <navonjohnlukose@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://patch.msgid.link/20261007191911.502428-1-navonjohnlukose@gmail.com
This commit is contained in:
Navon John Lukose 2026-10-08 03:52:31 +05:30 committed by Andi Shyti
parent 4906001042
commit e7d5d642c0
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1 changed files with 14 additions and 1 deletions
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15
drivers/i2c/busses/i2c-designware-master.c
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@ -378,7 +378,7 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
{
struct i2c_msg *msgs = dev->msgs;
u32 intr_mask;
int tx_limit, rx_limit;
int tx_limit, rx_limit, rx_tl;
u32 buf_len = dev->tx_buf_len;
u8 *buf = dev->tx_buf;
bool need_restart = false;
@ -484,6 +484,19 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
if (dev->msg_err)
intr_mask = 0;
/*
* Size the RX FIFO threshold to the reads already queued, so the
* controller raises one RX_FULL for the whole burst instead of one per
* received byte. While messages remain to be queued, cap it so RX_FULL
* still arrives in time to drain the FIFO and let the next TX_EMPTY
* queue the rest.
*/
rx_tl = dev->rx_outstanding;
if (dev->msg_write_idx < dev->msgs_num)
rx_tl = min_t(int, rx_tl, dev->rx_fifo_depth / 2);
regmap_write(dev->map, DW_IC_RX_TL, rx_tl ? rx_tl - 1 : 0);
__i2c_dw_write_intr_mask(dev, intr_mask);
}