Russell, On Sat, Aug 8, 2015 at 9:10 AM, Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> wrote: > Given the TDMS clock, audio sample rate, and the N parameter, we can > calculate the CTS value for the audio clock regenerator (ACR) using the > following calculation given in the HDMI specification: > > CTS = ftdms * N / (128 * fs) > > The specification says that the CTS value is an average value, which is > true if the source hardware measures it. Where source hardware needs it > to be programmed, it is particularly difficult to alternate it between > two values correctly to ensure that we achieve a correct "average" > fractional value at the sink. > > Also, there's the problem that our "ftdms" is not a fully accurate > value; it is rounded to a kHz value. This introduces an unnecessary > (and harmless) fractional value into the above equation for combinations > like 148.5MHz/1.001 for 44100Hz - we still calculate the correct CTS > value. > > Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx> > --- > drivers/gpu/drm/bridge/dw_hdmi.c | 92 +++++++--------------------------------- > 1 file changed, 16 insertions(+), 76 deletions(-) If you take my feedback about your "drm: bridge/dw_hdmi: adjust pixel clock values in N calculation" patch [1], all this math just works out to "cts = pixel_clk / 1000". ...but doing the math does future proof us a bit, so it seems like a good idea. Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Tested-by: Douglas Anderson <dianders@xxxxxxxxxxxx> [1] https://patchwork.kernel.org/patch/6975221/ _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
