From ce352550327b394f3072a07c9cd9d27af9276f15 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Fri, 20 Sep 2013 10:14:23 +0300 Subject: [PATCH] drm/i915: Fix unclaimed register access due to delayed VGA memory disable MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit VGA registers live inside the power well on HSW, so in order to write the VGA MSR register we need the power well to be on. We really must write to the register to properly clear the VGA_MSR_MEM_EN enable bit, even if all VGA registers get zeroed when the power well is down. It seems that the implicit zeroing done by the power well is not enough to propagate the VGA_MSR_MEM_EN bit to whomever is actually responsible for the memory decode ranges. If we leave VGA memory decode enabled, and then turn off the power well, all VGA memory reads will return zeroes. But if we first disable VGA memory deocde and then turn off the power well, VGA memory reads return all ones, indicating that the access wasn't claimed by anyone. For the vga arbiter to function correctly the IGD must not claim the VGA memory accesses. Previously we were doing the VGA_MSR register access while the power well was excplicitly powered up during driver init. But ever since commit 6e1b4fdad5157bb9e88777d525704aba24389bee Author: Ville Syrjälä Date: Thu Sep 5 20:40:52 2013 +0300 drm/i915: Delay disabling of VGA memory until vgacon->fbcon handoff is done we delay the VGA memory disable until fbcon has initialized, and so there's a possibility that the power well got turned off during the fbcon modeset. Also vgacon_save_screen() will need the power well to be on to be able to read the VGA memory. So immediately after enabling the power well during init grab a refence for VGA purposes, and after all the VGA handling is done, release it. v2: Add intel_display_power_put() for the num_pipes==0 case Signed-off-by: Ville Syrjälä Reviewed-by: Paulo Zanoni [danvet: Fix up the patch wiggle screw-up that I've done and which Paulo catched. Also polish spelling in the patch headline.] Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_dma.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c index aa69c735298e..e172624f8818 100644 --- a/drivers/gpu/drm/i915/i915_dma.c +++ b/drivers/gpu/drm/i915/i915_dma.c @@ -1326,13 +1326,18 @@ static int i915_load_modeset_init(struct drm_device *dev) intel_init_power_well(dev); + /* Keep VGA alive until i915_disable_vga_mem() */ + intel_display_power_get(dev, POWER_DOMAIN_VGA); + intel_modeset_gem_init(dev); /* Always safe in the mode setting case. */ /* FIXME: do pre/post-mode set stuff in core KMS code */ dev->vblank_disable_allowed = 1; - if (INTEL_INFO(dev)->num_pipes == 0) + if (INTEL_INFO(dev)->num_pipes == 0) { + intel_display_power_put(dev, POWER_DOMAIN_VGA); return 0; + } ret = intel_fbdev_init(dev); if (ret) @@ -1358,6 +1363,7 @@ static int i915_load_modeset_init(struct drm_device *dev) * vgacon_save_screen() works during the handover. */ i915_disable_vga_mem(dev); + intel_display_power_put(dev, POWER_DOMAIN_VGA); /* Only enable hotplug handling once the fbdev is fully set up. */ dev_priv->enable_hotplug_processing = true; -- 2.20.1