Hi Maxime,
On 5 January 2018 at 21:03, Maxime Ripard maxime.ripard@free-electrons.com wrote:
On Fri, Jan 05, 2018 at 09:44:39AM +1100, Jonathan Liu wrote:
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.
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.
Ok. I have added amended the commit message with explanation for v3.
Regards, Jonathan