On Thu, Jan 09, 2014 at 11:00:28AM +0530, akash.goel@xxxxxxxxx wrote:
> From: Akash Goel <akash.goel@xxxxxxxxx>
>
> There is a conflict seen when requesting the kernel to reserve
> the physical space used for the stolen area. This is because
> as somehow the start/base location of the Parent region
> of Stolen area which is PCI Bus 0000:00 is not coinciding with
> the start of Stolen area and is conflicting with it. For ex.
> from the device memory map info provided by '/proc/iomem',
> we have seen that somehow a region of PCI Bus 0000:00 is being
> shown to start from 0x7b000001,
> i.e. (7b000001-ffffffff : PCI Bus 0000:00) & not from
> 0x7b000000. And the stolen base is coming as 0x7b000000,
> thus there is a conflict & stolen area remains unused by driver.
> So to circumvent this issue we adjust the base of stolen area by
> 1 byte when registering it with the kernel.
> Otherwise if we don't resolve this conflict or don't remove the
> conflict error check from the driver, the stolen area will remain
> disabled.
>
> Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_stolen.c | 27 ++++++++++++++++++++++++---
> 1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index 1a24e84..29b3693 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -82,9 +82,30 @@ static unsigned long i915_stolen_to_physical(struct drm_device *dev)
> r = devm_request_mem_region(dev->dev, base, dev_priv->gtt.stolen_size,
> "Graphics Stolen Memory");
> if (r == NULL) {
> - DRM_ERROR("conflict detected with stolen region: [0x%08x - 0x%08x]\n",
> - base, base + (uint32_t)dev_priv->gtt.stolen_size);
> - base = 0;
> + /* One more attempt but this time requesting region from
> + * base + 1, as we have seen that this resolves the region
> + * conflict with the PCI Bus.
> + * This is because as somehow the start/base location of
> + * the Parent region of Stolen area which is PCI Bus 0000:00
> + * is not coinciding with the start of Stolen area and is
> + * conflicting with it. For ex. from the device memory map
> + * info provided by '/proc/iomem', we have seen that somehow
> + * a region of PCI Bus 0000:00 is being shown to start from
> + * 0x7b000001, i.e. (7b000001-ffffffff : PCI Bus 0000:00).
> + * And the stolen base is coming as 0x7b000000, thus there is a
> + * conflict and stolen memory remains unused by the driver.
> + * So to circumvent this issue we adjust the base of stolen
> + * area by 1 when registering it with the kernel.
> + */
I think this comment can be shortened a bit:
/*
* BIOS w/a: Some BIOS wrap stolen in the root PCI bus,
* but have an off-by-one error. Hence retry the
* reservation starting from 1 instead of 0.
*/
Curious readers can then bring up the full details with git blame. Also
note that we now prefer the multi-line comment delimiters /* and */ on
separate lines.
Cheers, Daniel
> + r = devm_request_mem_region(dev->dev, base + 1,
> + dev_priv->gtt.stolen_size - 1,
> + "Graphics Stolen Memory");
> + if (r == NULL) {
> + DRM_ERROR("conflict detected with stolen region:"\
> + "[0x%08x - 0x%08x]\n",
> + base, base + (uint32_t)dev_priv->gtt.stolen_size);
> + base = 0;
> + }
> }
>
> return base;
> --
> 1.8.5.2
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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