Re: [PATCH] drm/i915: Fix not finding the VBT when it overlaps with OPREGION_ASLE_EXT

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sun, 25 Dec 2016, Hans de Goede <hdegoede@redhat.com> wrote:
> If there is no OPREGION_ASLE_EXT then a VBT stored in mailbox #4 may
> use the ASLE_EXT parts of the opregion. Adjust the vbt_size calculation
> for a vbt in mailbox #4 for this.
>
> This fixes the driver not finding the VBT on a jumper ezpad mini3
> cherrytrail tablet.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
> Note even with this fixed the panel still does not work with 4.9,
> but it does with drm-intel-next-queued :) I believe the missing bit in
> 4.9 is the "drm/915: Parsing the missed out DTD fields from the VBT"
> commit, but I've not verified this.
> ---
>  drivers/gpu/drm/i915/intel_opregion.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_opregion.c b/drivers/gpu/drm/i915/intel_opregion.c
> index f4429f6..eff35ae 100644
> --- a/drivers/gpu/drm/i915/intel_opregion.c
> +++ b/drivers/gpu/drm/i915/intel_opregion.c
> @@ -982,7 +982,9 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
>  			opregion->vbt_size = vbt_size;
>  		} else {
>  			vbt = base + OPREGION_VBT_OFFSET;
> -			vbt_size = OPREGION_ASLE_EXT_OFFSET - OPREGION_VBT_OFFSET;
> +			vbt_size = (mboxes & MBOX_ASLE_EXT) ?
> +				OPREGION_ASLE_EXT_OFFSET : OPREGION_SIZE;
> +			vbt_size -= OPREGION_VBT_OFFSET;

First, I want a big fat warning comment about what's going on
here. Otherwise someone's bound to "fix" this later on.

Second, per the spec, the ASLE ext mailbox is 1k in size, and there's a
1k reserved region at the end. We probably shouldn't allow VBT to extend
over there. But hey, per the spec we also shouldn't allow VBT to extend
over mailbox #5 either. So if you can't be bothered with that, neither
will I.


BR,
Jani.



>  			if (intel_bios_is_valid_vbt(vbt, vbt_size)) {
>  				DRM_DEBUG_KMS("Found valid VBT in ACPI OpRegion (Mailbox #4)\n");
>  				opregion->vbt = vbt;

-- 
Jani Nikula, Intel Open Source Technology Center