From f9dcb0dfee98406c9c64e1aad10af427d644b78f Mon Sep 17 00:00:00 2001 From: Paulo Zanoni Date: Wed, 11 Dec 2013 18:50:10 -0200 Subject: [PATCH] drm/i915: touch VGA MSR after we enable the power well Fixes regression introduced by: commit bf51d5e2cda5d36d98e4b46ac7fca9461e512c41 Author: Paulo Zanoni Date: Wed Jul 3 17:12:13 2013 -0300 drm/i915: switch disable_power_well default value to 1 The bug I'm seeing can be reproduced with: - Have vgacon configured/enabled - Make sure the power well gets disabled, then enabled. You can check this by seeing the messages print by hsw_set_power_well - Stop your display manager - echo 0 > /sys/class/vtconsole/vtcon1/bind I can easily reproduce this by blacklising snd_hda_intel and booting with eDP+HDMI. If you do this and then look at dmesg, you'll see we're printing infinite "Unclaimed register" messages. This is happening because we're stuck on an infinite loop inside console_unlock(), which is calling many functions from vgacon.c. And the code that's triggering the error messages is from vgacon_set_cursor_size(). After we re-enable the power well, every time we read/write the VGA address 0x3d5 we get an "unclaimed register" interrupt (ERR_INT) and print error messages. If we write anything to the VGA MSR register (it doesn't really matter which value you write to bit 0), any reads/writes to 0x3d5 _don't_ trigger the "unclaimed register" errors anymore (even if MSR bit 0 is zero). So what happens with the current code is that when we unbind i915 and bind vgacon, we call console_unlock(). Function console_unlock() is responsible for printing any messages that were supposed to be print when the console was locked, so it calls the TTY layer, which calls the console layer, which calls vgacon to print the messages. At this point, vgacon eventually calls vgacon_set_cursor_size(), which touches 0x3d5, which triggers unclaimed register interrupts. The problem is that when we get these interrupts, we print the error messages, so we add more work to console_unlock(), which will try to print it again, and then call vgacon again, trigger a new interrupt, which will put more stuff to the buffer, and then we'll be stuck at console_unlock() forever. If you patch intel_uncore.c to not print anything when we detect unclaimed registers, we won't get into the console_unlock() infinite loop and the driver unbind will work just fine. We will still be getting interrupts every time vgacon touches those registers, but we will survive. This is a valid experiment, but IMHO it's not the real fix: if we don't print any error messages we will still keep getting the interrupts, and if we disable ERR_INT we won't get the interrupt anymore, but we will also stop getting all the other error interrupts. I talked about this problem with the HW engineer and his recommendation is "So don't do any VGA I/O or memory access while the power well is disabled, and make to re-program MSR after enabling the power well and before using VGA I/O or memory accesses.". Notice that this is just a partial fix to fd.o #67813. This fixes the case where the power well is already enabled when we unbind, not when it's disabled when we unbind. V2: - Rebase (first version was sent in September). V3: - Complete rewrite of the same fix: smaller implementation, improved commit message. Testcase: igt/drv_module_reload Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67813 Signed-off-by: Paulo Zanoni Reviewed-by: Damien Lespiau Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_pm.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c index d8fb00a..3cd521f 100644 --- a/drivers/gpu/drm/i915/intel_pm.c +++ b/drivers/gpu/drm/i915/intel_pm.c @@ -30,6 +30,7 @@ #include "intel_drv.h" #include "../../../platform/x86/intel_ips.h" #include +#include #include #include @@ -5686,6 +5687,20 @@ static void hsw_power_well_post_enable(struct drm_i915_private *dev_priv) struct drm_device *dev = dev_priv->dev; unsigned long irqflags; + /* + * After we re-enable the power well, if we touch VGA register 0x3d5 + * we'll get unclaimed register interrupts. This stops after we write + * anything to the VGA MSR register. The vgacon module uses this + * register all the time, so if we unbind our driver and, as a + * consequence, bind vgacon, we'll get stuck in an infinite loop at + * console_unlock(). So make here we touch the VGA MSR register, making + * sure vgacon can keep working normally without triggering interrupts + * and error messages. + */ + vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO); + outb(inb(VGA_MSR_READ), VGA_MSR_WRITE); + vga_put(dev->pdev, VGA_RSRC_LEGACY_IO); + if (IS_BROADWELL(dev)) { spin_lock_irqsave(&dev_priv->irq_lock, irqflags); I915_WRITE(GEN8_DE_PIPE_IMR(PIPE_B), -- 2.7.4