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From 92c64493f41092185230c552c277b42bf6113140 Mon Sep 17 00:00:00 2001
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From: Jani Nikula <jani.nikula@intel.com>
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Date: Mon, 21 Oct 2013 10:52:07 +0300
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Subject: [PATCH 3/5] drm/i915/dp: workaround BIOS eDP bpp clamping issue
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This isn't a real fix to the problem, but rather a stopgap measure while
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trying to find a proper solution.
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There are several laptops out there that fail to light up the eDP panel
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in UEFI boot mode. They seem to be mostly IVB machines, including but
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apparently not limited to Dell XPS 13, Asus TX300, Asus UX31A, Asus
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UX32VD, Acer Aspire S7. They seem to work in CSM or legacy boot.
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The difference between UEFI and CSM is that the BIOS provides a
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different VBT to the kernel. The UEFI VBT typically specifies 18 bpp and
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1.62 GHz link for eDP, while CSM VBT has 24 bpp and 2.7 GHz link. We end
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up clamping to 18 bpp in UEFI mode, which we can fit in the 1.62 Ghz
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link, and for reasons yet unknown fail to light up the panel.
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Dithering from 24 to 18 bpp itself seems to work; if we use 18 bpp with
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2.7 GHz link, the eDP panel lights up. So essentially this is a link
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speed issue, and *not* a bpp clamping issue.
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The bug raised its head since
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commit 657445fe8660100ad174600ebfa61536392b7624
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Author: Daniel Vetter <daniel.vetter@ffwll.ch>
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Date: Sat May 4 10:09:18 2013 +0200
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Revert "drm/i915: revert eDP bpp clamping code changes"
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which started clamping bpp *before* computing the link requirements, and
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thus affecting the required bandwidth. Clamping after the computations
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kept the link at 2.7 GHz.
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Even though the BIOS tells us to use 18 bpp through the VBT, it happily
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boots up at 24 bpp and 2.7 GHz itself! Use this information to
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selectively ignore the VBT provided value.
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We can't ignore the VBT eDP bpp altogether, as there are other laptops
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that do require the clamping to be used due to EDID reporting higher bpp
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than the panel can support.
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Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=59841
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Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67950
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Tested-by: Ulf Winkelvos <ulf@winkelvos.de>
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Tested-by: jkp <jkp@iki.fi>
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CC: stable@vger.kernel.org
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Signed-off-by: Jani Nikula <jani.nikula@intel.com>
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Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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---
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drivers/gpu/drm/i915/intel_dp.c | 20 ++++++++++++++++++++
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1 file changed, 20 insertions(+)
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diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
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index 3aed1fe..07eb447 100644
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--- a/drivers/gpu/drm/i915/intel_dp.c
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+++ b/drivers/gpu/drm/i915/intel_dp.c
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@@ -1371,6 +1371,26 @@ static void intel_dp_get_config(struct intel_encoder *encoder,
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}
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pipe_config->adjusted_mode.flags |= flags;
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+
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+ if (is_edp(intel_dp) && dev_priv->vbt.edp_bpp &&
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+ pipe_config->pipe_bpp > dev_priv->vbt.edp_bpp) {
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+ /*
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+ * This is a big fat ugly hack.
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+ *
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+ * Some machines in UEFI boot mode provide us a VBT that has 18
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+ * bpp and 1.62 GHz link bandwidth for eDP, which for reasons
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+ * unknown we fail to light up. Yet the same BIOS boots up with
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+ * 24 bpp and 2.7 GHz link. Use the same bpp as the BIOS uses as
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+ * max, not what it tells us to use.
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+ *
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+ * Note: This will still be broken if the eDP panel is not lit
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+ * up by the BIOS, and thus we can't get the mode at module
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+ * load.
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+ */
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+ DRM_DEBUG_KMS("pipe has %d bpp for eDP panel, overriding BIOS-provided max %d bpp\n",
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+ pipe_config->pipe_bpp, dev_priv->vbt.edp_bpp);
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+ dev_priv->vbt.edp_bpp = pipe_config->pipe_bpp;
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+ }
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}
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static void intel_disable_dp(struct intel_encoder *encoder)
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--
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1.8.3.1
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