Re: [PATCH] media: qcom: camss: configure C-PHY in the new csiphy_stream_on()

[George Neacsu]

Hi Anusha,

One units issue showed up while testing this on X1E80100.

camss_get_link_freq(..., cphy=true) returns the V4L2 C-PHY link
frequency. The media documentation defines link frequency as the bus
frequency, explicitly not the symbol rate; its C-PHY pixel-rate formula
also has the factor of two that makes the C-PHY symbol rate twice the
V4L2 link frequency.

For the SP11 IMX681, the exact Windows/QTI sensor mode programs PLL2
for a 2.400 Gsym/s C-PHY rate (19.2 MHz * 375 / 3). The same 68-write
mode programming was also observed live under KD on this machine.
camss_get_link_freq() returns the corresponding 1.200 GHz V4L2 link
frequency.

phy_mipi_cphy_get_default_config_for_hsclk() takes the high-speed symbol
rate, so passing link_freq directly here fills hs_clk_rate with
1.2 Gsym/s rather than 2.4 Gsym/s. I think this wants:

    phy_mipi_cphy_get_default_config_for_hsclk((u64)link_freq * 2,
                                                num_lanes, cphy_cfg);

I instrumented that path on X1E and get link=1200000000 Hz and
symbol=2400000000 sym/s. Capture succeeds with those values.

The qcom provider then needs to keep those units distinct too; I have a
separate comment on that patch.

Thanks,
George