On 08/27/2014 01:54 PM, Runyan, Arthur J wrote:
:-) We pulled most of the mobile functions from the bridge chip into the main
chip, so that same backlight code might well have been there.
From sandybridge onwards I see that hardware will override the PWM signal to
inactive (0 if backlight polarity is active high, 1 if active low) when PWM is
disabled (PWM control bit 31 = 0). I don't have anything older than
sandybridge to look at, and of course there could always be some hidden bug
that prevents the override from kicking in.
Just enabling/disabling the PWM control bit will reproduce the issue on
VLV. I have not tested on other platforms.
Clint
-----Original Message-----
From: Daniel Vetter [mailto:daniel.vet...@ffwll.ch] On Behalf Of Daniel Vetter
Sent: Tuesday, August 26, 2014 2:52 AM
To: Runyan, Arthur J
Cc: Jani Nikula; Taylor, Clinton A; Ville Syrjälä;
Intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915/dp: Backlight PWM enable before BL
Enable assert
On Fri, Aug 22, 2014 at 05:12:25PM +0000, Runyan, Arthur J wrote:
I'll check it out. I haven't heard any complaint about this before, but
it may be one of those things that started back on i745 and never got
documented.
Only i855 and later started to have native lvds with all the surrounding
stuff, before there's only bridge chips that did all the magic. So won't
be quite _that_ old ;-)
Cheers, Daniel
-----Original Message-----
From: Jani Nikula [mailto:jani.nik...@linux.intel.com]
Sent: Friday, August 22, 2014 6:07 AM
To: Taylor, Clinton A; Ville Syrjälä; Runyan, Arthur J
Cc: Intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915/dp: Backlight PWM enable before BL
Enable assert
+Art
On Thu, 21 Aug 2014, Clint Taylor <clinton.a.tay...@intel.com> wrote:
There is also a need to add this delay when turning off the PWM enable
bit through intel_panel_disable_backlight(). If the PWM enable bit is
turned off while the PWM signal is high then the signal remains high. If
the bit is turned off when the signal is low the PWM will remain low.
Since we don't know the current state of the PWM signal we must set the
duty_cycle to 0, wait PWM_CYCLE_DELAY, and then turn off the enable bit.
[citation needed]
Really, I want this in the specs if this is true.
Actually it might be better if we never turn off the PWM enable bit in
intel_panel_disable_backlight() and we just use the duty cycle register
to control the PWM.
Art, any feedback on these two?
BR,
Jani.
So I guess your approach is the simplest option here.
_intel_edp_backlight_on(intel_dp);
}
@@ -4256,9 +4257,10 @@ intel_dp_init_panel_power_sequencer(struct drm_device
*dev,
assign_final(t11_t12);
#undef assign_final
+#define PWM_CYCLE_DELAY 5
Shoduln't this be calculated from the PWM frequqncy? Not sure what a PWM
cycle here is exactly. Just one full period of the signal?
The PWM cycle in this case turns out to be 1 full cycle of the PWM
waveform though it depends on which display core clock (128 or
25Mhz(S0ix) is being used. Since we only care about the minimum elapsed
time to meet the panel specification a value of 5ms will work even
though more or less PWM cycles would take place before the BL_ENABLE is
asserted. I would prefer not to add complexity to switch between panel
timings for normal and S0ix display clock modes. How often does the
backlight get enabled while in S0ix?
Also would be nice to have a comment in the code explaining what this is
and why we need to add it to the delay.
Sure, As you may have noticed in other patches I really like comments.
#define get_delay(field) (DIV_ROUND_UP(final.field, 10))
intel_dp->panel_power_up_delay = get_delay(t1_t3);
- intel_dp->backlight_on_delay = get_delay(t8);
+ intel_dp->backlight_on_delay = get_delay(t8) + PWM_CYCLE_DELAY;
intel_dp->backlight_off_delay = get_delay(t9);
intel_dp->panel_power_down_delay = get_delay(t10);
intel_dp->panel_power_cycle_delay = get_delay(t11_t12);
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 3abc915..ad6fcc1 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -556,6 +556,7 @@ struct intel_dp {
bool want_panel_vdd;
unsigned long last_power_cycle;
unsigned long last_power_on;
+ unsigned long last_backlight_on;
unsigned long last_backlight_off;
struct notifier_block edp_notifier;
--
1.8.3.2
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Jani Nikula, Intel Open Source Technology Center
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