linux-kernel - Re: [BUG] rc1 rc2 rc3 not bootable - black screen after kernel loading

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Date:	Thu, 24 Jul 2014 16:20:25 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Martin Kepplinger <martink@...teo.de>
cc:	Daniel Vetter <ffwll.ch@...gle.com>,
	Zhang Rui <rui.zhang@...el.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-media@...r.kernel.org
Subject: Re: [BUG] rc1 rc2 rc3 not bootable - black screen after kernel
 loading

On Thu, 24 Jul 2014, Martin Kepplinger wrote:
> Am 2014-06-30 12:39, schrieb Martin Kepplinger:
> > back to aaeb2554337217dfa4eac2fcc90da7be540b9a73 as the first bad
> > commit. why is this not revertable exactly? how can I show a complete
> > list of commits this merge introduces?
> > 
> 
> It seems that _nobody_ is running a simple 32 bit i915 (acer) laptop.
> rc6 is still unusable. Black screen directly after kernel-loading. no
> change since rc1.
> 
> Seems like I won't be able to use 3.16. I'm happy to test patches and am
> happy for any advice what to do, when time permits.

Martin, I know nothing about aaeb25543372 and why it should be relevant,
but if you're having rc1..rc6 32-bit i915 black screens, please try this
patch that Daniel Vetter put in his fixes queue on Monday, which I'm
hoping will reach Linus for -rc7.

Hugh

[PATCH] drm/i915: fix freeze with blank screen booting highmem

x86_64 boots and displays fine, but booting x86_32 with CONFIG_HIGHMEM
has frozen with a blank screen throughout 3.16-rc on this ThinkPad T420s,
with i915 generation 6 graphics.

Fix 9d0a6fa6c5e6 ("drm/i915: add render state initialization"): kunmap()
takes struct page * argument, not virtual address.  Which the compiler
kindly points out, if you use the appropriate u32 *batch, instead of
silencing it with a void *.

Why did bisection lead decisively to nearby 229b0489aa75 ("drm/i915:
add null render states for gen6, gen7 and gen8")?  Because the u32
deposited at that virtual address by the previous stub failed the
PageHighMem test, and so caused no harm.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 drivers/gpu/drm/i915/i915_gem_render_state.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- 3.16-rc/drivers/gpu/drm/i915/i915_gem_render_state.c	2014-06-16 00:28:52.384076465 -0700
+++ linux/drivers/gpu/drm/i915/i915_gem_render_state.c	2014-07-21 20:10:03.824481521 -0700
@@ -31,7 +31,7 @@
 struct i915_render_state {
 	struct drm_i915_gem_object *obj;
 	unsigned long ggtt_offset;
-	void *batch;
+	u32 *batch;
 	u32 size;
 	u32 len;
 };
@@ -80,7 +80,7 @@ free:
 
 static void render_state_free(struct i915_render_state *so)
 {
-	kunmap(so->batch);
+	kunmap(kmap_to_page(so->batch));
 	i915_gem_object_ggtt_unpin(so->obj);
 	drm_gem_object_unreference(&so->obj->base);
 	kfree(so);
--
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