2013/5/5 Chris Wilson <chris at chris-wilson.co.uk>: > On Fri, May 03, 2013 at 05:23:42PM -0300, Paulo Zanoni wrote: >> From: Paulo Zanoni <paulo.r.zanoni at intel.com> >> >> With this, that 338 can finally become the correct 337500. >> >> Due to the change we need to adjust the intel_dp_aux_ch function to >> set the correct value, so adjust the division and also use >> DIV_ROUND_CLOSEST instead of the old "round down" behavior because the >> spec says the value "should be programmed to get as close as possible >> to the ideal rate of 2MHz". > > Can you please demonstrate an instance where this code produces a > different value? And only then correct the constants. I use the 337500 value on the next patch, when setting the ips_linetime value. The correct frequency is 337500, not 338000. ips_linetime = DIV_ROUND_CLOSEST(mode->htotal * 1000 * 8, intel_ddi_get_cdclk_freq); For a mode with htotal of 2640 [0] we'll have: (i) (2640 * 1000 * 8) / 338000 = 62.48, resulting in 62 and (ii) (2640 * 1000 * 8) / 337500 = 62.57 resulting in 63. For the case inside intel_dp.c: Previously we were using 338. So with the old formula we were writing 338/2 = 169 to the register. And 337500 / 169 = 1997.04 (we use 337500 here because it's the real clock value). With the new value of 337500/2000 we'll have 168.75, which is 168 on the round-down case and 169 on the round-closest case. If we write 168 to the register, 337500 / 168 = 2008.92, and 2008.92 is more distant from 2000 than 1997.04. So with this patch we're changing the formula but still writing the same correct value to the DP AUX register. [0]: That's 1920x1080 at 50Hz on my DP monitor. > -Chris > > -- > Chris Wilson, Intel Open Source Technology Centre -- Paulo Zanoni
