[03/18] drm/i915: Fix location of stolen memory register for SandyBridge+

Commit Message

Chris Wilson Oct. 19, 2012, 5:03 p.m. UTC

A few of the earlier registers where enlarged and so the Base Data of
Stolen Memory Register (BDSM) was pushed to 0xb0.

Signed-off-by: Chris Wilson <[e-mail]>
Reviewed-by: Jesse Barnes <[e-mail]>
---
 drivers/gpu/drm/i915/i915_gem_stolen.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Comments

Ben Widawsky Oct. 26, 2012, 9:58 p.m. UTC | #1

On Fri, 19 Oct 2012 18:03:09 +0100
Chris Wilson <[e-mail]> wrote:

> A few of the earlier registers where enlarged and so the Base Data of
> Stolen Memory Register (BDSM) was pushed to 0xb0.
> 
> Signed-off-by: Chris Wilson <[e-mail]>
> Reviewed-by: Jesse Barnes <[e-mail]>

This patch seems irrelevant to me. I have a i915_stolen_to_phys which
already looks correct (git blame shows you last updated it in April).

Can you help unconfuse me?

> ---
>  drivers/gpu/drm/i915/i915_gem_stolen.c |   12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c
> b/drivers/gpu/drm/i915/i915_gem_stolen.c index a01ff74..d023ed6 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -63,7 +63,14 @@ static unsigned long
> i915_stolen_to_physical(struct drm_device *dev)
>  	 * its value of TOLUD.
>  	 */
>  	base = 0;
> -	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> +	if (INTEL_INFO(dev)->gen >= 6) {
> +		/* Read Base Data of Stolen Memory Register (BDSM)
> directly.
> +		 * Note that there is also a MCHBAR miror at
> 0x1080c0 or
> +		 * we could use device 2:0x5c instead.
> +		*/
> +		pci_read_config_dword(pdev, 0xB0, &base);
> +		base &= ~4095; /* lower bits used for locking
> register */
> +	} else if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
>  		/* Read Graphics Base of Stolen Memory directly */
>  		pci_read_config_dword(pdev, 0xA4, &base);
>  #if 0
> @@ -172,6 +179,9 @@ int i915_gem_init_stolen(struct drm_device *dev)
>  	if (dev_priv->mm.stolen_base == 0)
>  		return 0;
>  
> +	DRM_DEBUG_KMS("found %d bytes of stolen memory at %08lx\n",
> +		      dev_priv->mm.gtt->stolen_size,
> dev_priv->mm.stolen_base); +
>  	/* Basic memrange allocator for stolen space */
>  	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);
>

Chris Wilson Oct. 28, 2012, 9:48 a.m. UTC | #2

On Fri, 26 Oct 2012 14:58:45 -0700, Ben Widawsky <[e-mail]> wrote:
> On Fri, 19 Oct 2012 18:03:09 +0100
> Chris Wilson <[e-mail]> wrote:
> 
> > A few of the earlier registers where enlarged and so the Base Data of
> > Stolen Memory Register (BDSM) was pushed to 0xb0.
> > 
> > Signed-off-by: Chris Wilson <[e-mail]>
> > Reviewed-by: Jesse Barnes <[e-mail]>
> 
> This patch seems irrelevant to me. I have a i915_stolen_to_phys which
> already looks correct (git blame shows you last updated it in April).
> 
> Can you help unconfuse me?

As the patch suggests the current registers being used by stolen-to-phys
are incorrect for SNB+.
-Chris

Ben Widawsky Oct. 28, 2012, 5:52 p.m. UTC | #3

On Sun, 28 Oct 2012 09:48:35 +0000
Chris Wilson <[e-mail]> wrote:

> On Fri, 26 Oct 2012 14:58:45 -0700, Ben Widawsky <[e-mail]>
> wrote:
> > On Fri, 19 Oct 2012 18:03:09 +0100
> > Chris Wilson <[e-mail]> wrote:
> > 
> > > A few of the earlier registers where enlarged and so the Base
> > > Data of Stolen Memory Register (BDSM) was pushed to 0xb0.
> > > 
> > > Signed-off-by: Chris Wilson <[e-mail]>
> > > Reviewed-by: Jesse Barnes <[e-mail]>
> > 
> > This patch seems irrelevant to me. I have a i915_stolen_to_phys
> > which already looks correct (git blame shows you last updated it in
> > April).
> > 
> > Can you help unconfuse me?
> 
> As the patch suggests the current registers being used by
> stolen-to-phys are incorrect for SNB+.
> -Chris
> 

Well no thanks to you, I found my confusion. Since I skipped patch 2 as
I don't care about gen2, this patch made no sense to me. It looks like
I need to go back and review patch 2 since among fixing detection for
gen2 you did a few other things such as changing the name
from i915_stolen_to_physical to i915_stolen_to_phys.

Ben Widawsky Nov. 2, 2012, 12:08 a.m. UTC | #4

On Sun, 28 Oct 2012 09:48:35 +0000
Chris Wilson <[e-mail]> wrote:

> On Fri, 26 Oct 2012 14:58:45 -0700, Ben Widawsky <[e-mail]> wrote:
> > On Fri, 19 Oct 2012 18:03:09 +0100
> > Chris Wilson <[e-mail]> wrote:
> > 
> > > A few of the earlier registers where enlarged and so the Base Data of
> > > Stolen Memory Register (BDSM) was pushed to 0xb0.
> > > 
> > > Signed-off-by: Chris Wilson <[e-mail]>
> > > Reviewed-by: Jesse Barnes <[e-mail]>
> > 
> > This patch seems irrelevant to me. I have a i915_stolen_to_phys which
> > already looks correct (git blame shows you last updated it in April).
> > 
> > Can you help unconfuse me?
> 
> As the patch suggests the current registers being used by stolen-to-phys
> are incorrect for SNB+.
> -Chris
> 

It looks like all you've done here is fix up the bug you left from
patch2.

Chris Wilson Nov. 2, 2012, 8:54 a.m. UTC | #5

On Thu, 1 Nov 2012 17:08:20 -0700, Ben Widawsky <[e-mail]> wrote:
> On Sun, 28 Oct 2012 09:48:35 +0000
> Chris Wilson <[e-mail]> wrote:
> 
> > On Fri, 26 Oct 2012 14:58:45 -0700, Ben Widawsky <[e-mail]> wrote:
> > > On Fri, 19 Oct 2012 18:03:09 +0100
> > > Chris Wilson <[e-mail]> wrote:
> > > 
> > > > A few of the earlier registers where enlarged and so the Base Data of
> > > > Stolen Memory Register (BDSM) was pushed to 0xb0.
> > > > 
> > > > Signed-off-by: Chris Wilson <[e-mail]>
> > > > Reviewed-by: Jesse Barnes <[e-mail]>
> > > 
> > > This patch seems irrelevant to me. I have a i915_stolen_to_phys which
> > > already looks correct (git blame shows you last updated it in April).
> > > 
> > > Can you help unconfuse me?
> > 
> > As the patch suggests the current registers being used by stolen-to-phys
> > are incorrect for SNB+.
> > -Chris
> > 
> 
> It looks like all you've done here is fix up the bug you left from
> patch2.
> 
> -- 
> Ben Widawsky, Intel Open Source Technology Center
From: Chris Wilson <[e-mail]>
Subject: Re: [Intel-gfx] [PATCH 02/18] drm/i915: Fix detection of stolen base for gen2
To: Ben Widawsky <[e-mail]>
Cc: [e-mail]
In-Reply-To: <[e-mail]>
References: <[e-mail]> <[e-mail]> <[e-mail]>

On Thu, 1 Nov 2012 16:51:02 -0700, Ben Widawsky <[e-mail]> wrote:
> On Fri, 19 Oct 2012 18:03:08 +0100
> Chris Wilson <[e-mail]> wrote:
> 
> > It was not until the G33 refresh, that a PCI config register was
> > introduced that explicitly said where the stolen memory was. Prior to
> > 865G there was not even a register that said where the end of usable
> > low memory was and where the stolen memory began (or ended depending
> > upon chipset). Before then, one has to look at the BIOS memory maps to
> > find the Top of Memory. Alas that is not exported by arch/x86 and so we
> > have to resort to disabling stolen memory on gen2 for the time being.
> > 
> > Signed-off-by: Chris Wilson <[e-mail]>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h        |    1 +
> >  drivers/gpu/drm/i915/i915_gem_stolen.c |   69 ++++++++++++++------------------
> >  2 files changed, 31 insertions(+), 39 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 4728d30..687f379 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -705,6 +705,7 @@ typedef struct drm_i915_private {
> >  		unsigned long gtt_start;
> >  		unsigned long gtt_mappable_end;
> >  		unsigned long gtt_end;
> > +		unsigned long stolen_base; /* limited to low memory (32-bit) */
> >  
> >  		struct io_mapping *gtt_mapping;
> >  		phys_addr_t gtt_base_addr;
> > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > index ada2e90..a01ff74 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > @@ -43,56 +43,43 @@
> >   * for is a boon.
> >   */
> >  
> > -#define PTE_ADDRESS_MASK		0xfffff000
> > -#define PTE_ADDRESS_MASK_HIGH		0x000000f0 /* i915+ */
> > -#define PTE_MAPPING_TYPE_UNCACHED	(0 << 1)
> > -#define PTE_MAPPING_TYPE_DCACHE		(1 << 1) /* i830 only */
> > -#define PTE_MAPPING_TYPE_CACHED		(3 << 1)
> > -#define PTE_MAPPING_TYPE_MASK		(3 << 1)
> > -#define PTE_VALID			(1 << 0)
> > -
> > -/**
> > - * i915_stolen_to_phys - take an offset into stolen memory and turn it into
> > - *                       a physical one
> > - * @dev: drm device
> > - * @offset: address to translate
> > - *
> > - * Some chip functions require allocations from stolen space and need the
> > - * physical address of the memory in question.
> > - */
> > -static unsigned long i915_stolen_to_phys(struct drm_device *dev, u32 offset)
> > +static unsigned long i915_stolen_to_physical(struct drm_device *dev)
> >  {
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  	struct pci_dev *pdev = dev_priv->bridge_dev;
> >  	u32 base;
> >  
> > -#if 0
> >  	/* On the machines I have tested the Graphics Base of Stolen Memory
> > -	 * is unreliable, so compute the base by subtracting the stolen memory
> > -	 * from the Top of Low Usable DRAM which is where the BIOS places
> > -	 * the graphics stolen memory.
> > +	 * is unreliable, so on those compute the base by subtracting the
> > +	 * stolen memory from the Top of Low Usable DRAM which is where the
> > +	 * BIOS places the graphics stolen memory.
> > +	 *
> > +	 * On gen2, the layout is slightly different with the Graphics Segment
> > +	 * immediately following Top of Memory (or Top of Usable DRAM). Note
> > +	 * it appears that TOUD is only reported by 865g, so we just use the
> > +	 * top of memory as determined by the e820 probe.
> > +	 *
> > +	 * XXX gen2 requires an unavailable symbol and 945gm fails with
> > +	 * its value of TOLUD.
> >  	 */
> > +	base = 0;
> >  	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> > -		/* top 32bits are reserved = 0 */
> > +		/* Read Graphics Base of Stolen Memory directly */
> >  		pci_read_config_dword(pdev, 0xA4, &base);
> > -	} else {
> > -		/* XXX presume 8xx is the same as i915 */
> > -		pci_bus_read_config_dword(pdev->bus, 2, 0x5C, &base);
> > -	}
> > -#else
> > -	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> > -		u16 val;
> > -		pci_read_config_word(pdev, 0xb0, &val);
> > -		base = val >> 4 << 20;
> > -	} else {
> > +#if 0
> > +	} else if (IS_GEN3(dev)) {
> >  		u8 val;
> > +		/* Stolen is immediately below Top of Low Usable DRAM */
> >  		pci_read_config_byte(pdev, 0x9c, &val);
> >  		base = val >> 3 << 27;
> > -	}
> > -	base -= dev_priv->mm.gtt->stolen_size;
> > +		base -= dev_priv->mm.gtt->stolen_size;
> > +	} else {
> > +		/* Stolen is immediately above Top of Memory */
> > +		base = max_low_pfn_mapped << PAGE_SHIFT;
> >  #endif
> > +	}
> >  
> > -	return base + offset;
> > +	return base;
> >  }
> >  
> 
> Comments on this below.
> 
> >  static void i915_warn_stolen(struct drm_device *dev)
> > @@ -117,7 +104,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> >  	if (!compressed_fb)
> >  		goto err;
> >  
> > -	cfb_base = i915_stolen_to_phys(dev, compressed_fb->start);
> > +	cfb_base = dev_priv->mm.stolen_base + compressed_fb->start;
> >  	if (!cfb_base)
> >  		goto err_fb;
> >  
> > @@ -130,7 +117,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> >  		if (!compressed_llb)
> >  			goto err_fb;
> >  
> > -		ll_base = i915_stolen_to_phys(dev, compressed_llb->start);
> > +		ll_base = dev_priv->mm.stolen_base + compressed_llb->start;
> >  		if (!ll_base)
> >  			goto err_llb;
> >  	}
> > @@ -149,7 +136,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> >  	}
> >  
> >  	DRM_DEBUG_KMS("FBC base 0x%08lx, ll base 0x%08lx, size %dM\n",
> > -		      cfb_base, ll_base, size >> 20);
> > +		      (long)cfb_base, (long)ll_base, size >> 20);
> >  	return;
> >  
> >  err_llb:
> > @@ -181,6 +168,10 @@ int i915_gem_init_stolen(struct drm_device *dev)
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  	unsigned long prealloc_size = dev_priv->mm.gtt->stolen_size;
> >  
> > +	dev_priv->mm.stolen_base = i915_stolen_to_physical(dev);
> > +	if (dev_priv->mm.stolen_base == 0)
> > +		return 0;
> > +
> >  	/* Basic memrange allocator for stolen space */
> >  	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);
> >  
> 
> Since I found viewing the diff difficult for this patch, I am going to
> write the before and after (with the #if 0 blocks removed):
> 
> Before:
>         if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
>                 u16 val;
>                 pci_read_config_word(pdev, 0xb0, &val);
>                 base = val >> 4 << 20;
>         } else {
>                 u8 val;
>                 pci_read_config_byte(pdev, 0x9c, &val);
>                 base = val >> 3 << 27;
>         }
>         base -= dev_priv->mm.gtt->stolen_size;
> 
> After:
>         base = 0;
>         if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
>                 /* Read Graphics Base of Stolen Memory directly */
>                 pci_read_config_dword(pdev, 0xA4, &base);
> 
> 
> I like that this is a simple helper now to calculate GSM Base. However,
> I am completely baffled by this patch. The read of 0xA4 did exist
> before, but was #if 0'd out appears to be the PCI capabilities pointer
> as of GEN6 (I won't check before that). The before code on the other
> hand at least looks correct for gen6 (BDSM - GGMS).
> 
> This seems like it will definitely break SNB+, which would be bad for
> bisection.

The code as it stands is broken on SNB (it only has a semblance of
working but the address it generates is random and points into active
system memory), so it seems immaterial as to whether it then remained
broken after this patch, with the benefit of then having individual
patches to address the later generations. To allay your fears, this can
be split into a preparatory patch to allow the routine to fail, and then
fail until each is fixed.
-Chris

Ben Widawsky Nov. 5, 2012, 1:53 p.m. UTC | #6

On Fri, 02 Nov 2012 08:54:39 +0000
Chris Wilson <[e-mail]> wrote:

> On Thu, 1 Nov 2012 17:08:20 -0700, Ben Widawsky <[e-mail]> wrote:
> > On Sun, 28 Oct 2012 09:48:35 +0000
> > Chris Wilson <[e-mail]> wrote:
> > 
> > > On Fri, 26 Oct 2012 14:58:45 -0700, Ben Widawsky <[e-mail]> wrote:
> > > > On Fri, 19 Oct 2012 18:03:09 +0100
> > > > Chris Wilson <[e-mail]> wrote:
> > > > 
> > > > > A few of the earlier registers where enlarged and so the Base Data of
> > > > > Stolen Memory Register (BDSM) was pushed to 0xb0.
> > > > > 
> > > > > Signed-off-by: Chris Wilson <[e-mail]>
> > > > > Reviewed-by: Jesse Barnes <[e-mail]>
> > > > 
> > > > This patch seems irrelevant to me. I have a i915_stolen_to_phys which
> > > > already looks correct (git blame shows you last updated it in April).
> > > > 
> > > > Can you help unconfuse me?
> > > 
> > > As the patch suggests the current registers being used by stolen-to-phys
> > > are incorrect for SNB+.
> > > -Chris
> > > 
> > 
> > It looks like all you've done here is fix up the bug you left from
> > patch2.
> > 
> > -- 
> > Ben Widawsky, Intel Open Source Technology Center
> From: Chris Wilson <[e-mail]>
> Subject: Re: [Intel-gfx] [PATCH 02/18] drm/i915: Fix detection of stolen base for gen2
> To: Ben Widawsky <[e-mail]>
> Cc: [e-mail]
> In-Reply-To: <[e-mail]>
> References: <[e-mail]> <[e-mail]> <[e-mail]>
> 
> On Thu, 1 Nov 2012 16:51:02 -0700, Ben Widawsky <[e-mail]> wrote:
> > On Fri, 19 Oct 2012 18:03:08 +0100
> > Chris Wilson <[e-mail]> wrote:
> > 
> > > It was not until the G33 refresh, that a PCI config register was
> > > introduced that explicitly said where the stolen memory was. Prior to
> > > 865G there was not even a register that said where the end of usable
> > > low memory was and where the stolen memory began (or ended depending
> > > upon chipset). Before then, one has to look at the BIOS memory maps to
> > > find the Top of Memory. Alas that is not exported by arch/x86 and so we
> > > have to resort to disabling stolen memory on gen2 for the time being.
> > > 
> > > Signed-off-by: Chris Wilson <[e-mail]>
> > > ---
> > >  drivers/gpu/drm/i915/i915_drv.h        |    1 +
> > >  drivers/gpu/drm/i915/i915_gem_stolen.c |   69 ++++++++++++++------------------
> > >  2 files changed, 31 insertions(+), 39 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > > index 4728d30..687f379 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > @@ -705,6 +705,7 @@ typedef struct drm_i915_private {
> > >  		unsigned long gtt_start;
> > >  		unsigned long gtt_mappable_end;
> > >  		unsigned long gtt_end;
> > > +		unsigned long stolen_base; /* limited to low memory (32-bit) */
> > >  
> > >  		struct io_mapping *gtt_mapping;
> > >  		phys_addr_t gtt_base_addr;
> > > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > index ada2e90..a01ff74 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > @@ -43,56 +43,43 @@
> > >   * for is a boon.
> > >   */
> > >  
> > > -#define PTE_ADDRESS_MASK		0xfffff000
> > > -#define PTE_ADDRESS_MASK_HIGH		0x000000f0 /* i915+ */
> > > -#define PTE_MAPPING_TYPE_UNCACHED	(0 << 1)
> > > -#define PTE_MAPPING_TYPE_DCACHE		(1 << 1) /* i830 only */
> > > -#define PTE_MAPPING_TYPE_CACHED		(3 << 1)
> > > -#define PTE_MAPPING_TYPE_MASK		(3 << 1)
> > > -#define PTE_VALID			(1 << 0)
> > > -
> > > -/**
> > > - * i915_stolen_to_phys - take an offset into stolen memory and turn it into
> > > - *                       a physical one
> > > - * @dev: drm device
> > > - * @offset: address to translate
> > > - *
> > > - * Some chip functions require allocations from stolen space and need the
> > > - * physical address of the memory in question.
> > > - */
> > > -static unsigned long i915_stolen_to_phys(struct drm_device *dev, u32 offset)
> > > +static unsigned long i915_stolen_to_physical(struct drm_device *dev)
> > >  {
> > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > >  	struct pci_dev *pdev = dev_priv->bridge_dev;
> > >  	u32 base;
> > >  
> > > -#if 0
> > >  	/* On the machines I have tested the Graphics Base of Stolen Memory
> > > -	 * is unreliable, so compute the base by subtracting the stolen memory
> > > -	 * from the Top of Low Usable DRAM which is where the BIOS places
> > > -	 * the graphics stolen memory.
> > > +	 * is unreliable, so on those compute the base by subtracting the
> > > +	 * stolen memory from the Top of Low Usable DRAM which is where the
> > > +	 * BIOS places the graphics stolen memory.
> > > +	 *
> > > +	 * On gen2, the layout is slightly different with the Graphics Segment
> > > +	 * immediately following Top of Memory (or Top of Usable DRAM). Note
> > > +	 * it appears that TOUD is only reported by 865g, so we just use the
> > > +	 * top of memory as determined by the e820 probe.
> > > +	 *
> > > +	 * XXX gen2 requires an unavailable symbol and 945gm fails with
> > > +	 * its value of TOLUD.
> > >  	 */
> > > +	base = 0;
> > >  	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> > > -		/* top 32bits are reserved = 0 */
> > > +		/* Read Graphics Base of Stolen Memory directly */
> > >  		pci_read_config_dword(pdev, 0xA4, &base);
> > > -	} else {
> > > -		/* XXX presume 8xx is the same as i915 */
> > > -		pci_bus_read_config_dword(pdev->bus, 2, 0x5C, &base);
> > > -	}
> > > -#else
> > > -	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> > > -		u16 val;
> > > -		pci_read_config_word(pdev, 0xb0, &val);
> > > -		base = val >> 4 << 20;
> > > -	} else {
> > > +#if 0
> > > +	} else if (IS_GEN3(dev)) {
> > >  		u8 val;
> > > +		/* Stolen is immediately below Top of Low Usable DRAM */
> > >  		pci_read_config_byte(pdev, 0x9c, &val);
> > >  		base = val >> 3 << 27;
> > > -	}
> > > -	base -= dev_priv->mm.gtt->stolen_size;
> > > +		base -= dev_priv->mm.gtt->stolen_size;
> > > +	} else {
> > > +		/* Stolen is immediately above Top of Memory */
> > > +		base = max_low_pfn_mapped << PAGE_SHIFT;
> > >  #endif
> > > +	}
> > >  
> > > -	return base + offset;
> > > +	return base;
> > >  }
> > >  
> > 
> > Comments on this below.
> > 
> > >  static void i915_warn_stolen(struct drm_device *dev)
> > > @@ -117,7 +104,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> > >  	if (!compressed_fb)
> > >  		goto err;
> > >  
> > > -	cfb_base = i915_stolen_to_phys(dev, compressed_fb->start);
> > > +	cfb_base = dev_priv->mm.stolen_base + compressed_fb->start;
> > >  	if (!cfb_base)
> > >  		goto err_fb;
> > >  
> > > @@ -130,7 +117,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> > >  		if (!compressed_llb)
> > >  			goto err_fb;
> > >  
> > > -		ll_base = i915_stolen_to_phys(dev, compressed_llb->start);
> > > +		ll_base = dev_priv->mm.stolen_base + compressed_llb->start;
> > >  		if (!ll_base)
> > >  			goto err_llb;
> > >  	}
> > > @@ -149,7 +136,7 @@ static void i915_setup_compression(struct drm_device *dev, int size)
> > >  	}
> > >  
> > >  	DRM_DEBUG_KMS("FBC base 0x%08lx, ll base 0x%08lx, size %dM\n",
> > > -		      cfb_base, ll_base, size >> 20);
> > > +		      (long)cfb_base, (long)ll_base, size >> 20);
> > >  	return;
> > >  
> > >  err_llb:
> > > @@ -181,6 +168,10 @@ int i915_gem_init_stolen(struct drm_device *dev)
> > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > >  	unsigned long prealloc_size = dev_priv->mm.gtt->stolen_size;
> > >  
> > > +	dev_priv->mm.stolen_base = i915_stolen_to_physical(dev);
> > > +	if (dev_priv->mm.stolen_base == 0)
> > > +		return 0;
> > > +
> > >  	/* Basic memrange allocator for stolen space */
> > >  	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);
> > >  
> > 
> > Since I found viewing the diff difficult for this patch, I am going to
> > write the before and after (with the #if 0 blocks removed):
> > 
> > Before:
> >         if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> >                 u16 val;
> >                 pci_read_config_word(pdev, 0xb0, &val);
> >                 base = val >> 4 << 20;
> >         } else {
> >                 u8 val;
> >                 pci_read_config_byte(pdev, 0x9c, &val);
> >                 base = val >> 3 << 27;
> >         }
> >         base -= dev_priv->mm.gtt->stolen_size;
> > 
> > After:
> >         base = 0;
> >         if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
> >                 /* Read Graphics Base of Stolen Memory directly */
> >                 pci_read_config_dword(pdev, 0xA4, &base);
> > 
> > 
> > I like that this is a simple helper now to calculate GSM Base. However,
> > I am completely baffled by this patch. The read of 0xA4 did exist
> > before, but was #if 0'd out appears to be the PCI capabilities pointer
> > as of GEN6 (I won't check before that). The before code on the other
> > hand at least looks correct for gen6 (BDSM - GGMS).
> > 
> > This seems like it will definitely break SNB+, which would be bad for
> > bisection.
> 
> The code as it stands is broken on SNB (it only has a semblance of
> working but the address it generates is random and points into active
> system memory), so it seems immaterial as to whether it then remained
> broken after this patch, with the benefit of then having individual
> patches to address the later generations. To allay your fears, this can
> be split into a preparatory patch to allow the routine to fail, and then
> fail until each is fixed.
> -Chris
> 

Please do allay my fears, and I can review it again. However in the
meantime, I disagree. The code seems correct to me as I said above (for
SNB, I haven't back-checked to previous generations). What I am looking
at now tells me that stolen memory base (which is located directly above
the GTT stolen memory) is defined by the 31:20 of offset 0xb0.
Similarly, we know the size of the stolen memory for the gtt ptes from
offset 0x50 (caculated previously), therefore the address certainly
isn't random. If there is a gap between the PTEs and the stolen
memory, then I agree it's somewhat problematic, but it still seems
better than what you changed it to.

Anyway, this is all in reference to patch 2 really since patch 3 fixes
the problem.

Patch

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
index a01ff74..d023ed6 100644
--- a/drivers/gpu/drm/i915/i915_gem_stolen.c
+++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
@@ -63,7 +63,14 @@  static unsigned long i915_stolen_to_physical(struct drm_device *dev)
 	 * its value of TOLUD.
 	 */
 	base = 0;
-	if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
+	if (INTEL_INFO(dev)->gen >= 6) {
+		/* Read Base Data of Stolen Memory Register (BDSM) directly.
+		 * Note that there is also a MCHBAR miror at 0x1080c0 or
+		 * we could use device 2:0x5c instead.
+		*/
+		pci_read_config_dword(pdev, 0xB0, &base);
+		base &= ~4095; /* lower bits used for locking register */
+	} else if (INTEL_INFO(dev)->gen > 3 || IS_G33(dev)) {
 		/* Read Graphics Base of Stolen Memory directly */
 		pci_read_config_dword(pdev, 0xA4, &base);
 #if 0
@@ -172,6 +179,9 @@  int i915_gem_init_stolen(struct drm_device *dev)
 	if (dev_priv->mm.stolen_base == 0)
 		return 0;
 
+	DRM_DEBUG_KMS("found %d bytes of stolen memory at %08lx\n",
+		      dev_priv->mm.gtt->stolen_size, dev_priv->mm.stolen_base);
+
 	/* Basic memrange allocator for stolen space */
 	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);