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Message-ID: <547C5890.2020306@aurabindo.in>
Date: Mon, 01 Dec 2014 17:31:20 +0530
From: Jay Aurabind <mail@...abindo.in>
To: Jani Nikula <jani.nikula@...ux.intel.com>,
Daniel Vetter <daniel.vetter@...el.com>,
David Airlie <airlied@...ux.ie>,
intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915 Trouble with minimum brightness
On 12/01/2014 03:04 PM, Jani Nikula wrote:
> On Fri, 28 Nov 2014, Jay Aurabind <mail@...abindo.in> wrote:
>> Hello all,
>>
>> I notice that some activity has been going on with the minimum value
>> of display brightness recently (e1c412e7575).
>>
>> But the minimum value thats currently chosen is not at all acceptable
>> for my eyes. My display is working perfectly without that restriction
>> on minimum intensity. I tend to stare at the screen a lot and the
>> current minimum settings is straining my eyes.
>>
>> Even if you say that it may not be good for the devices, I still
>> insist, because I want my *display* to fail first, not my eyes. So
>> please try providing a way for the needy users to override this
>> minimum settings. I hope adding a module parameter would be easy fix.
>>
>> Something like this: ? (I dont call myself a kernel programmer yet,
>> just scratching the surface)
>>
>>
>> Provide provision for users to disable restriction on minimum brightness
>> value introduced in:
>>
>> commit e1c412e75754ab7b7002f3e18a2652d999c40d4b
>> Author: Jani Nikula <jani.nikula@...el.com>
>> Date: Wed Nov 5 14:46:31 2014 +0200
>>
>> drm/i915: safeguard against too high minimum brightness
>>
>> There are systems which work reliably without restriction on minimum
>> value of display brightness. Also the arbitrary value may be too high
>> for many users as well.
>
> Please file a new bug at [1], reference this mail, and attach
> /sys/kernel/debug/dri/0/i915_opregion.
Thank you for the response. But the file you mentioned to attach seems to be
a binary file, because I'm getting lot of junk characters. Is this normal ?
>
> The minimum value is chosen and provided by the OEM. There's still some
> open questions about the interpretation of the value though (which lead
> to the commit you referenced), so I'm hesitant to make changes before we
> have those cleared up.
From a user's point of view, the reason many people and myself stick to linux
is the flexibility it provides and the power the user has, and when
you introduce a new policy without an easy "roll back" to get back the
previous "mechanism", I would like to let you know that it matters.
> In general I am not fond of adding new module parameters for tuning
> things. Every new knob is another point of failure that we need to test,
> and they are pretty much part of the ABI we can't easily drop or change.
Would it be difficult to remove a parameter, if it is marked "experimental" ?
Is there a fix this without changing ABI ? I mean can you make this policy
apply only on those hardware which seems to have a problem with the value of
minimum backlight? Since they are the minority, why should a policy for fixing them
affect the rest of us ?
--
Thanks and Regards,
Aurabindo J
>
> BR,
> Jani.
>
> [1] https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=DRM/Intel
>
>
>>
>> Signed-off-by: Aurabindo J <mail@...abindo.in>
>> ---
>> drivers/gpu/drm/i915/i915_drv.h | 1 +
>> drivers/gpu/drm/i915/i915_params.c | 6 ++++++
>> drivers/gpu/drm/i915/intel_panel.c | 14 ++++++++++----
>> 3 files changed, 17 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index 16a6f6d..55d2ead 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -2213,6 +2213,7 @@ struct i915_params {
>> int disable_power_well;
>> int enable_ips;
>> int invert_brightness;
>> + int restrict_min_brightness;
>> int enable_cmd_parser;
>> /* leave bools at the end to not create holes */
>> bool enable_hangcheck;
>> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>> index c91cb20..0601c2a 100644
>> --- a/drivers/gpu/drm/i915/i915_params.c
>> +++ b/drivers/gpu/drm/i915/i915_params.c
>> @@ -46,6 +46,7 @@ struct i915_params i915 __read_mostly = {
>> .prefault_disable = 0,
>> .reset = true,
>> .invert_brightness = 0,
>> + .restrict_min_brightness = 1,
>> .disable_display = 0,
>> .enable_cmd_parser = 1,
>> .disable_vtd_wa = 0,
>> @@ -155,6 +156,11 @@ MODULE_PARM_DESC(invert_brightness,
>> "to dri-devel@...ts.freedesktop.org, if your machine needs it. "
>> "It will then be included in an upcoming module version.");
>>
>> +module_param_named(restrict_min_brightness, i915.restrict_min_brightness, int, 0600);
>> +MODULE_PARM_DESC(restrict_min_brightness,
>> + "Restrict minimum brightness "
>> + "(-1 disable restriction, 0 value from VBT, 1 arbitrary value )");
>> +
>> module_param_named(disable_display, i915.disable_display, bool, 0600);
>> MODULE_PARM_DESC(disable_display, "Disable display (default: false)");
>>
>> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
>> index 41b3be2..def9f4e 100644
>> --- a/drivers/gpu/drm/i915/intel_panel.c
>> +++ b/drivers/gpu/drm/i915/intel_panel.c
>> @@ -1109,10 +1109,16 @@ static u32 get_backlight_min_vbt(struct intel_connector *connector)
>> * against this by letting the minimum be at most (arbitrarily chosen)
>> * 25% of the max.
>> */
>> - min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64);
>> - if (min != dev_priv->vbt.backlight.min_brightness) {
>> - DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n",
>> - dev_priv->vbt.backlight.min_brightness, min);
>> + if (i915.restrict_min_brightness < 0)
>> + min = 0;
>> + else if (i915.restrict_min_brightness == 0)
>> + min = dev_priv->vbt.backlight.min_brightness;
>> + else {
>> + min = clamp_t(int, dev_priv->vbt.backlight.min_brightness, 0, 64);
>> + if (min != dev_priv->vbt.backlight.min_brightness) {
>> + DRM_DEBUG_KMS("clamping VBT min backlight %d/255 to %d/255\n",
>> + dev_priv->vbt.backlight.min_brightness, min);
>> + }
>> }
>>
>> /* vbt value is a coefficient in range [0..255] */
>> --
>> 2.1.3
>>
>>
>>
>>
>>
>
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