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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - Backlight flicker after suspend on certain Intel CherryTrail tablets"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111095#c21">Comment # 21</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - Backlight flicker after suspend on certain Intel CherryTrail tablets"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111095">bug 111095</a>
from <span class="vcard"><a class="email" href="mailto:jwrdegoede@fedoraproject.org" title="Hans de Goede <jwrdegoede@fedoraproject.org>"> <span class="fn">Hans de Goede</span></a>
</span></b>
<pre>(In reply to Jani Nikula from <a href="show_bug.cgi?id=111095#c13">comment #13</a>)
<span class="quote">> Hmm, I think the VBT says it uses the CPU PWM.</span >
I have access to both a Miix320 and an Irbis TW90 for testing, both my models
use a DSI panel. AFAIK DSI panels always either the Crystal Cove PMIC PWM, or
the LPSS PWM (which is part of the SoC).
I guess you are basing this "I think the VBT says it uses the CPU PWM" on the
dev_priv->vbt.dsi.config->pwm_blc bit ? When that is PPS_BLC_SOC then the LPSS
PWM is used, not the PWM which is part of the display controller. Also see:
drivers/gpu/drm/i915/display/intel_panel.c which has:
} else if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
if (connector->base.connector_type == DRM_MODE_CONNECTOR_DSI) {
panel->backlight.setup = pwm_setup_backlight;
panel->backlight.enable = pwm_enable_backlight;
panel->backlight.disable = pwm_disable_backlight;
panel->backlight.set = pwm_set_backlight;
panel->backlight.get = pwm_get_backlight;
} else {
...
And pwm_setup_backlight() does:
/* Get the PWM chip for backlight control */
panel->backlight.pwm = pwm_get(dev->dev, "pwm_backlight");
Which means it uses the pwm subsystem to talk to either the CRC or LPSS pwm
controller.
So AFAICT dumping the registers of the display-block PWM controller does not
provide any useful info here. I actually wonder if the displayblock on CHT
devices has the PWM controller at all.</pre>
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