Hi Fabio,
Am Dienstag, den 02.09.2014, 10:31 -0300 schrieb Fabio Estevam:
For debug purposes it is useful to know how far away the generated pixelclock is from the desired rate, so print the amount of error.
After adding this patch and with debug enabled we have:
imx-ipuv3 2400000.ipu: disp 0: panel size = 1920 x 1080 imx-ipuv3 2400000.ipu: Clocks: IPU 264000000Hz DI 24000000Hz Needed 138500000Hz imx-ipuv3 2400000.ipu: IPU clock can give 132000000 with divider 2, error -4.3% imx-ipuv3 2400000.ipu: Want 138500000Hz IPU 264000000Hz DI 138500000Hz using DI, 138500000Hz, error 0.0% imx-ipuv3 2400000.ipu: disp 1: panel size = 1024 x 768 imx-ipuv3 2400000.ipu: Clocks: IPU 264000000Hz DI 64999999Hz Needed 65000000Hz imx-ipuv3 2400000.ipu: Want 65000000Hz IPU 264000000Hz DI 64999999Hz using DI, 64999999Hz, error 0.9%
As this example shows ...
[...]
- dev_dbg(di->ipu->dev, "Want %luHz IPU %luHz DI %luHz using %s, %luHz\n",
- error = (clk_get_rate(di->clk_di_pixel) / (clkgen0 >> 4)) / (sig->pixelclock / 1000);
- dev_dbg(di->ipu->dev, "Want %luHz IPU %luHz DI %luHz using %s, %luHz, error %d.%u%%\n", sig->pixelclock, clk_get_rate(di->clk_ipu), clk_get_rate(di->clk_di), clk == di->clk_di ? "DI" : "IPU",
clk_get_rate(di->clk_di_pixel) / (clkgen0 >> 4));
clk_get_rate(di->clk_di_pixel) / (clkgen0 >> 4),(signed)(error - 1000) / 10, error % 10);
... this only works for positive deviations. If error < 1000, error % 10 will return the wrong value and for 990 < error < 1000 the sign is missing.
Also you are losing a lot of presicion. the real error in the example is more like 0.000002%, so I wonder how useful this really is.
regards Philipp