media: tc358743: Increase FIFO trigger level to 374

The existing fixed value of 16 worked for UYVY 720P60 over
2 lanes at 594MHz, or UYVY 1080P60 over 4 lanes. (RGB888
1080P60 needs 6 lanes at 594MHz).
It doesn't allow for lower resolutions to work as the FIFO
underflows.

374 is required for 1080P24 or 1080P30 UYVY over 2 lanes @
972Mbit/s, but >374 means that the FIFO underflows on 1080P50
UYVY over 2 lanes @ 972Mbit/s.

Whilst it would be nice to compute it, the required information
isn't published by Toshiba.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

diff --git a/drivers/media/i2c/tc358743.c b/drivers/media/i2c/tc358743.c
index b87db3de20db142aa0283ea2ec15dd88150ed527..ddba8c392ead483619a6b3870bebac288726631c 100644 (file)
--- a/drivers/media/i2c/tc358743.c
+++ b/drivers/media/i2c/tc358743.c
@@ -1972,8 +1972,19 @@ static int tc358743_probe_of(struct tc358743_state *state)
        state->pdata.refclk_hz = clk_get_rate(refclk);
        state->pdata.ddc5v_delay = DDC5V_DELAY_100_MS;
        state->pdata.enable_hdcp = false;
-       /* A FIFO level of 16 should be enough for 2-lane 720p60 at 594 MHz. */
-       state->pdata.fifo_level = 16;
+       /*
+        * Ideally the FIFO trigger level should be set based on the input and
+        * output data rates, but the calculations required are buried in
+        * Toshiba's register settings spreadsheet.
+        * A value of 16 works with a 594Mbps data rate for 720p60 (using 2
+        * lanes) and 1080p60 (using 4 lanes), but fails when the data rate
+        * is increased, or a lower pixel clock is used that result in CSI
+        * reading out faster than the data is arriving.
+        *
+        * A value of 374 works with both those modes at 594Mbps, and with most
+        * modes on 972Mbps.
+        */
+       state->pdata.fifo_level = 374;
        /*
         * The PLL input clock is obtained by dividing refclk by pll_prd.
         * It must be between 6 MHz and 40 MHz, lower frequency is better.