On Fri, Jan 05, 2018 at 09:44:39AM +1100, Jonathan Liu wrote: > Hi Maxime, > > On 5 January 2018 at 06:56, Maxime Ripard > <maxime.rip...@free-electrons.com> wrote: > > On Tue, Dec 26, 2017 at 10:12:25PM +1100, Jonathan Liu wrote: > >> We should check if the best match has been set before comparing it. > >> > >> Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support") > >> Signed-off-by: Jonathan Liu <net...@gmail.com> > >> --- > >> drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c > >> b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c > >> index dc332ea56f6c..4d235e5ea31c 100644 > >> --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c > >> +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c > >> @@ -102,7 +102,7 @@ static int sun4i_tmds_determine_rate(struct clk_hw *hw, > >> goto out; > >> } > >> > >> - if (abs(rate - rounded / i) < > >> + if (!best_parent || abs(rate - rounded / i) < > > > > Why is that causing any issue? > > > > If best_parent is set to 0... > > > >> abs(rate - best_parent / best_div)) { > > > > ... the value returned here is going to be rate, which is going to be > > higher than the first part of the comparison meaning ... > > > >> best_parent = rounded; > > > > ... that best_parent is going to be set there. > > Consider the following: > rate = 83500000 > rounded = ideal * 2 > > It is possible that if "rounded = clk_hw_round_rate(parent, ideal)" > gives high enough values that the condition "abs(rate - rounded / i) < > abs(rate - best_parent / best_div)" is never met. > > Then you can end up with: > req->rate = 0 > req->best_parent_rate = 0 > req->best_parent_hw = ... > > Also, the sun4i_tmds_calc_divider function has a similar check.
Ok. That explanation must be part of your commit log, or at least which problem you're trying to address and in which situation it will trigger. Maxime -- Maxime Ripard, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
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