Re: [PATCH] Revert "drm/i915: skip modeset if compatible for everyone."

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 19 Nov 2015, Jani Nikula <jani.nikula@intel.com> wrote:
> This reverts
>
> commit 6764e9f8724f1231b4deac53b9a82286ac0830e7
> Author: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Date:   Thu Aug 27 15:44:06 2015 +0200
>
>     drm/i915: skip modeset if compatible for everyone.
>
> Bring back the i915.fastboot module parameter, disabled by default, due
> to backlight regression on Chromebook Pixel 2015.
>
> Apparently the firmware of the Chromebook in question enables the panel
> but disables backlight to avoid a brief garbage scanout upon loading the
> kernel/module. With fastboot, we leave the backlight untouched, in this
> case disabled. The user would have to do a modeset (i.e. not just crank
> up the brightness) to enable the backlight.
>
> There is no clean fix readily available, so get back to the drawing
> board by reverting.
>
> [N.B. The reference below is for when the thread was included on public
> lists, and some of the context had already been dropped by then.]
>
> Reported-and-tested-by: Olof Johansson <olof@lixom.net>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> References: http://marc.info/?i=CAKMK7uES7xk05ki92oeX6gmvZWAh9f2vL7yz=6T+fGK9J3X7cQ@mail.gmail.com
> Fixes: 6764e9f8724f ("drm/i915: skip modeset if compatible for everyone.")
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Pushed to drm-intel-fixes with IRC acks from Daniel and Maarten (*). I
took the liberty of adding Tested-by from Olof, as he reported reverting
the bad commit fixes the issue for him, and it's a clean revert.

BR,
Jani.


(*) In truth Maarten said "sigh", I presumed short for Sighed-off-by,
which I took to be close enough to Acked-by.


> ---
>  drivers/gpu/drm/i915/i915_drv.h      | 1 +
>  drivers/gpu/drm/i915/i915_params.c   | 5 +++++
>  drivers/gpu/drm/i915/intel_display.c | 3 ++-
>  3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 6db4e76dc7eb..a47e0f4fab56 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2656,6 +2656,7 @@ struct i915_params {
>  	int enable_cmd_parser;
>  	/* leave bools at the end to not create holes */
>  	bool enable_hangcheck;
> +	bool fastboot;
>  	bool prefault_disable;
>  	bool load_detect_test;
>  	bool reset;
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 0f5af02e90e9..835d6099c769 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -41,6 +41,7 @@ struct i915_params i915 __read_mostly = {
>  	.preliminary_hw_support = IS_ENABLED(CONFIG_DRM_I915_PRELIMINARY_HW_SUPPORT),
>  	.disable_power_well = -1,
>  	.enable_ips = 1,
> +	.fastboot = 0,
>  	.prefault_disable = 0,
>  	.load_detect_test = 0,
>  	.reset = true,
> @@ -139,6 +140,10 @@ MODULE_PARM_DESC(disable_power_well,
>  module_param_named_unsafe(enable_ips, i915.enable_ips, int, 0600);
>  MODULE_PARM_DESC(enable_ips, "Enable IPS (default: true)");
>  
> +module_param_named(fastboot, i915.fastboot, bool, 0600);
> +MODULE_PARM_DESC(fastboot,
> +	"Try to skip unnecessary mode sets at boot time (default: false)");
> +
>  module_param_named_unsafe(prefault_disable, i915.prefault_disable, bool, 0600);
>  MODULE_PARM_DESC(prefault_disable,
>  	"Disable page prefaulting for pread/pwrite/reloc (default:false). "
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 9a1c1d48a7d8..46015af47c20 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13236,7 +13236,8 @@ static int intel_atomic_check(struct drm_device *dev,
>  		if (ret)
>  			return ret;
>  
> -		if (intel_pipe_config_compare(state->dev,
> +		if (i915.fastboot &&
> +		    intel_pipe_config_compare(state->dev,
>  					to_intel_crtc_state(crtc->state),
>  					pipe_config, true)) {
>  			crtc_state->mode_changed = false;

-- 
Jani Nikula, Intel Open Source Technology Center
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