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Subject: Re: [4/5] drm/i915: Auto detect DPCD backlight support by default
To:     Lyude Paul <lyude@redhat.com>, intel-gfx@lists.freedesktop.org
Cc:     David Airlie <airlied@linux.ie>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org
References: <20191122231616.2574-5-lyude@redhat.com>
From:   Perr Yuan <pyuan@redhat.com>
Message-ID: <3ba84125-ab4c-e1a7-cb74-b65638f1c2d5@redhat.com>
Date:   Mon, 23 Dec 2019 02:20:36 -0500
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On 11/22/19 6:16 PM, Lyude Paul wrote:
> Turns out we actually already have some companies, such as Lenovo,
> shipping machines with AMOLED screens that don't allow controlling the
> backlight through the usual PWM interface and only allow controlling it
> through the standard EDP DPCD interface. One example of one of these
> laptops is the X1 Extreme 2nd Generation.
> 
> Since we've got systems that need this turned on by default now to have
> backlight controls working out of the box, let's start auto-detecting it
> for systems by default based on what the VBT tells us. We do this by
> changing the default value for the enable_dpcd_backlight module param
> from 0 to -1.
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_params.c | 2 +-
>   drivers/gpu/drm/i915/i915_params.h | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 1dd1f3652795..31eed60c167e 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -172,7 +172,7 @@ i915_param_named_unsafe(inject_probe_failure, uint, 0400,
>   
>   i915_param_named(enable_dpcd_backlight, int, 0600,
>   	"Enable support for DPCD backlight control"
> -	"(-1=use per-VBT LFP backlight type setting, 0=disabled [default], 1=enabled)");
> +	"(-1=use per-VBT LFP backlight type setting [default], 0=disabled, 1=enabled)");
>   
>   #if IS_ENABLED(CONFIG_DRM_I915_GVT)
>   i915_param_named(enable_gvt, bool, 0400,
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index 31b88f297fbc..a79d0867f77a 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -64,7 +64,7 @@ struct drm_printer;
>   	param(int, reset, 3) \
>   	param(unsigned int, inject_probe_failure, 0) \
>   	param(int, fastboot, -1) \
> -	param(int, enable_dpcd_backlight, 0) \
> +	param(int, enable_dpcd_backlight, -1) \
>   	param(char *, force_probe, CONFIG_DRM_I915_FORCE_PROBE) \
>   	param(unsigned long, fake_lmem_start, 0) \
>   	/* leave bools at the end to not create holes */ \
> 

Tested-by:Perry Yuan <pyuan@redhat.com>