On Thu, Feb 12, 2015 at 01:24:05PM +0100, Sascha Hauer wrote: > On Thu, Feb 12, 2015 at 06:39:45PM +0800, Liu Ying wrote: > > On Thu, Feb 12, 2015 at 10:33:56AM +0100, Sascha Hauer wrote: > > > On Thu, Feb 12, 2015 at 02:01:24PM +0800, Liu Ying wrote: > > > > If no best divider is normally found, we will try to use the maximum divider. > > > > We should not set the parent clock rate to be 1Hz by force for being rounded. > > > > Instead, we should take the maximum divider as a base and calculate a correct > > > > parent clock rate for being rounded. > > > > > > Please add an explanation why you think the current code is wrong and > > > what this actually fixes, maybe an example? > > > > The MIPI DSI panel's pixel clock rate is 26.4MHz and it's derived from PLL5 on > > the MX6DL SabreSD board. > > > > These are the clock tree summaries with or without the patch applied: > > 1) With the patch applied: > > pll5_bypass_src 1 1 24000000 0 0 > > pll5 1 1 844800048 0 0 > > pll5_bypass 1 1 844800048 0 0 > > pll5_video 1 1 844800048 0 0 > > pll5_post_div 1 1 211200012 0 0 > > pll5_video_div 1 1 211200012 0 0 > > ipu1_di0_pre_sel 1 1 211200012 0 0 > > ipu1_di0_pre 1 1 26400002 0 0 > > ipu1_di0_sel 1 1 26400002 0 0 > > ipu1_di0 1 1 26400002 0 0 > > > > 2) Without the patch applied: > > pll5_bypass_src 1 1 24000000 0 0 > > pll5 1 1 648000000 0 0 > > pll5_bypass 1 1 648000000 0 0 > > pll5_video 1 1 648000000 0 0 > > pll5_post_div 1 1 162000000 0 0 > > pll5_video_div 1 1 40500000 0 0 > > ipu1_di0_pre_sel 1 1 40500000 0 0 > > ipu1_di0_pre 1 1 20250000 0 0 > > ipu1_di0_sel 1 1 20250000 0 0 > > ipu1_di0 1 1 20250000 0 0 > > This seems to be broken since: > > | commit b11d282dbea27db1788893115dfca8a7856bf205 > | Author: Tomi Valkeinen <tomi.valkeinen@xxxxxx> > | Date: Thu Feb 13 12:03:59 2014 +0200 > | > | clk: divider: fix rate calculation for fractional rates > > This patch fixed a case when clk_set_rate(clk_round_rate(rate)) resulted > in a lower frequency than clk_round_rate(rate) returned. > > Since then the MULT_ROUND_UP in clk_divider_bestdiv() is inconsistent to > the rest of the divider. Maybe this should be a simple rate * i now, but > I'm unsure what side effects this has. > > I think your patch only fixes the behaviour in your case by accident, > it's not a correct fix for this issue. Well, it's defined that: new_rate = clk_round_rate(clk, rate); returns the rate which you would get if you did: clk_set_rate(clk, rate); new_rate = clk_get_rate(clk); The reasoning here is that clk_round_rate() gives you a way to query what rate you would get if you were to ask for the rate to be set, without effecting a change in the hardware. The idea that you should call clk_round_rate() first before clk_set_rate() and pass the returned rounded rate into clk_set_rate() is really idiotic given that. Please don't do it, and please remove code which does it, and in review comment on it. Thanks. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
