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From: Jani Nikula <jani.nikula@linux.intel.com>
To: Grant Likely <grant.likely@secretlab.ca>,
        David Woodhouse <dwmw2@infradead.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, Matthew Garrett <mjg@redhat.com>
Subject: Re: [PATCH] i915: Quirk out disconnected backlight
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Date: Mon, 17 Sep 2012 11:03:30 +0300
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On Fri, 14 Sep 2012, Grant Likely <grant.likely@secretlab.ca> wrote:
> On Fri, Sep 14, 2012 at 2:12 PM, David Woodhouse <dwmw2@infradead.org> wrote:
>> See https://bugzilla.redhat.com/show_bug.cgi?id=752595
>
> In that bug you mention that the intel backlight sets a bogus max of
> '1' when a backlight isn't present. I saw that too here. Here's the
> offending code:
>
> u32 intel_panel_get_max_backlight(struct drm_device *dev)
> {
>         struct drm_i915_private *dev_priv = dev->dev_private;
>         u32 max;
>
>         max = i915_read_blc_pwm_ctl(dev_priv);
>         if (max == 0) {
>                 /* XXX add code here to query mode clock or hardware clock
>                  * and program max PWM appropriately.
>                  */
>                 pr_warn_once("fixme: max PWM is zero\n");
>                 return 1;
>         }
>
> I used a quirk in my patch, but I could instead change the driver to
> bail here instead of trying to limp along.

Hi Grant, please try v3.6-rc6 that does exactly that with:

commit 28dcc2d60cb570d9f549c329b2f51400553412a1
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Mon Sep 3 16:25:12 2012 +0300

    drm/i915: do not expose a dysfunctional backlight interface to userspace

Does that fix it for you?


BR,
Jani.