Re: [PATCH 3/3] drm/i915: DSI: select correct PWM controller to use based on the VBT

Ville Syrjälä
2019-11-19T15:47:25Z

On Tue, Nov 19, 2019 at 04:18:18PM +0100, Hans de Goede wrote:
> At least Bay Trail (BYT) and Cherry Trail (CHT) devices can use 1 of 2
> different PWM controllers for controlling the LCD's backlight brightness.
> Either the one integrated into the PMIC or the one integrated into the
> SoC (the 1st LPSS PWM controller).
>
> So far in the LPSS code on BYT we have skipped registering the LPSS PWM
> controller "pwm_backlight" lookup entry when a Crystal Cove PMIC is
> present, assuming that in this case the PMIC PWM controller will be used.
>
> On CHT we have been relying on only 1 of the 2 PWM controllers being
> enabled in the DSDT at the same time; and always registered the lookup.
>
> So far this has been working, but the correct way to determine which PWM
> controller needs to be used is by checking a bit in the VBT table and
> recently I've learned about 2 different BYT devices:
> Point of View MOBII TAB-P800W
> Acer Switch 10 SW5-012
>
> Which use a Crystal Cove PMIC, yet the LCD is connected to the SoC/LPSS
> PWM controller (and the VBT correctly indicates this), so here our old
> heuristics fail.
>
> This commit fixes using the wrong PWM controller on these devices by
> calling pwm_get() for the right PWM controller based on the
> VBT dsi.config.pwm_blc bit.
>
> Note this is part of a series which contains 2 other patches which renames
> the PWM lookup for the 1st SoC/LPSS PWM from "pwm_backlight" to
> "pwm_pmic_backlight" and the PWM lookup for the Crystal Cove PMIC PWM
> from "pwm_backlight" to "pwm_pmic_backlight".
>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
> drivers/gpu/drm/i915/display/intel_panel.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c
> index bc14e9c0285a..ddcf311d1114 100644
> --- a/drivers/gpu/drm/i915/display/intel_panel.c
> +++ b/drivers/gpu/drm/i915/display/intel_panel.c
> @@ -1840,13 +1840,22 @@ static int pwm_setup_backlight(struct intel_connector *connector,
> enum pipe pipe)
> {
> struct drm_device *dev = connector->base.dev;
> + struct drm_i915_private *dev_priv = to_i915(dev);
> struct intel_panel *panel = &connector->panel;
> + const char *desc;
> int retval;
>
> - /* Get the PWM chip for backlight control */
> - panel->backlight.pwm = pwm_get(dev->dev, "pwm_backlight");
> + /* Get the right PWM chip for DSI backlight according to VBT */
> + if (dev_priv->vbt.dsi.config->pwm_blc == PPS_BLC_PMIC) {
> + panel->backlight.pwm = pwm_get(dev->dev, "pwm_pmic_backlight");
> + desc = "PMIC";
> + } else {
> + panel->backlight.pwm = pwm_get(dev->dev, "pwm_soc_backlight");
> + desc = "SoC";
> + }

Might we want the same thing for the panel enable gpio?

> +
> if (IS_ERR(panel->backlight.pwm)) {
> - DRM_ERROR("Failed to own the pwm chip\n");
> + DRM_ERROR("Failed to get the %s PWM chip\n", desc);
> panel->backlight.pwm = NULL;
> return -ENODEV;
> }
> @@ -1873,6 +1882,7 @@ static int pwm_setup_backlight(struct intel_connector *connector,
> CRC_PMIC_PWM_PERIOD_NS);
> panel->backlight.enabled = panel->backlight.level != 0;
>
> + DRM_INFO("Using %s PWM for LCD backlight control\n", desc);
> return 0;
> }
>
> --
> 2.23.0

--
Ville Syrjälä
Intel