linux-kernel - Re: [PATCH] drm/i915: disable CPU PWM also on LPT/SPT backlight disable

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Date:	Tue, 29 Sep 2015 15:49:15 +0300
From:	Jani Nikula <jani.nikula@...el.com>
To:	Huang Ying <ying.huang@...ux.intel.com>
Cc:	kernel test robot <ying.huang@...el.com>, lkp@...org,
	LKML <linux-kernel@...r.kernel.org>,
	Clint Taylor <Clinton.A.Taylor@...el.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"intel-gfx\@lists.freedesktop.org" <intel-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/i915: disable CPU PWM also on LPT/SPT backlight disable


Also adding Cc: intel-gfx, please include that in follow-ups.

Thanks,
Jani.

On Tue, 29 Sep 2015, Jani Nikula <jani.nikula@...el.com> wrote:
> Although we don't support or enable CPU PWM with LPT/SPT based systems,
> it may have been enabled prior to loading the driver. Disable the CPU
> PWM on LPT/SPT backlight disable to avoid warnings on LCPLL disable.
>
> The issue has been present on BDW since BDW enabling, but was recently
> introduced on HSW with
>
> commit 437b15b8017e0d946453c10794b0c5d4591cf180
> Author: Jani Nikula <jani.nikula@...el.com>
> Date:   Fri Sep 4 16:55:13 2015 +0300
>
>     drm/i915: use pch backlight override on hsw too
>
> Reference: http://mid.gmane.org/87y4frhwsn.fsf@yhuang-dev.intel.com
> Reported-by: kernel test robot <ying.huang@...el.com>
> Signed-off-by: Jani Nikula <jani.nikula@...el.com>
> ---
>  drivers/gpu/drm/i915/intel_panel.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index dd71e7f139e3..c9c94d05f3dd 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -731,6 +731,20 @@ static void lpt_disable_backlight(struct intel_connector *connector)
>  
>  	intel_panel_actually_set_backlight(connector, 0);
>  
> +	/*
> +	 * Although we don't support or enable CPU PWM with LPT/SPT based
> +	 * systems, it may have been enabled prior to loading the
> +	 * driver. Disable to avoid warnings on LCPLL disable.
> +	 *
> +	 * This needs rework if we need to add support for CPU PWM on PCH split
> +	 * platforms.
> +	 */
> +	tmp = I915_READ(BLC_PWM_CPU_CTL2);
> +	if (tmp & BLM_PWM_ENABLE) {
> +		DRM_DEBUG_KMS("cpu backlight was enabled, disabling\n");
> +		I915_WRITE(BLC_PWM_CPU_CTL2, tmp & ~BLM_PWM_ENABLE);
> +	}
> +
>  	tmp = I915_READ(BLC_PWM_PCH_CTL1);
>  	I915_WRITE(BLC_PWM_PCH_CTL1, tmp & ~BLM_PCH_PWM_ENABLE);
>  }
> -- 
> 2.1.4
>

-- 
Jani Nikula, Intel Open Source Technology Center
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