Messages in this thread | | | From | Jonathan Liu <> | Date | Fri, 5 Jan 2018 09:44:39 +1100 | Subject | Re: [PATCH v2 1/3] drm/sun4i: hdmi: Check for unset best_parent in sun4i_tmds_determine_rate |
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Hi Maxime,
On 5 January 2018 at 06:56, Maxime Ripard <maxime.ripard@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 <net147@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.
Regards, Jonathan
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