Re: [PATCH for v4.2] Revert "drm/i915: Allow parsing of variable size child device entries from VBT"

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Aug 18, 2015 at 09:58:57AM -0700, Daniel Vetter wrote:
> On Tue, Aug 18, 2015 at 2:33 AM, Jani Nikula <jani.nikula@intel.com> wrote:
> > This reverts
> >
> > commit 047fe6e6db9161e69271f56daaafdaf2add023b1
> > Author: David Weinehall <david.weinehall@linux.intel.com>
> > Date:   Tue Aug 4 16:55:52 2015 +0300
> >
> >     drm/i915: Allow parsing of variable size child device entries from VBT
> >
> > That commit is not valid for v4.2, however it will be valid for v4.3. It
> > was simply queued too early.
> 
> Nope, this patch from David also incidentally fixes a regression from
> 90e4f1592bb6e82f6690f0e05a8aadc which is why I merged it to.

What regression?

> If you
> want to revert this, you need to revert more (and with that also break
> BSW).
> 
> Isn't there a more minimal fix we can do for 4.2?
> -Daniel
> 
> >
> > The referenced regressing commit is just fine until the size of struct
> > common_child_dev_config changes, and that won't happen until
> > v4.3. Indeed, the expected size checks here rely on the increased size
> > of the struct, breaking new platforms.
> >
> > Fixes: 047fe6e6db91 ("drm/i915: Allow parsing of variable size child device entries from VBT")
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: David Weinehall <david.weinehall@linux.intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >
> > ---
> >
> > There was another patch from David increasing the size of the struct
> > [1], but that then regresses sdvo mapping parsing. It's the simplest to
> > just revert and fix this up properly for v4.3.
> >
> > [1] http://mid.gmane.org/20150813131415.GO6150@boom
> > ---
> >  drivers/gpu/drm/i915/intel_bios.c | 27 ++++-----------------------
> >  1 file changed, 4 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> > index 3dcd59e694db..198fc3c3291b 100644
> > --- a/drivers/gpu/drm/i915/intel_bios.c
> > +++ b/drivers/gpu/drm/i915/intel_bios.c
> > @@ -1075,34 +1075,15 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
> >         const union child_device_config *p_child;
> >         union child_device_config *child_dev_ptr;
> >         int i, child_device_num, count;
> > -       u8 expected_size;
> > -       u16 block_size;
> > +       u16     block_size;
> >
> >         p_defs = find_section(bdb, BDB_GENERAL_DEFINITIONS);
> >         if (!p_defs) {
> >                 DRM_DEBUG_KMS("No general definition block is found, no devices defined.\n");
> >                 return;
> >         }
> > -       if (bdb->version < 195) {
> > -               expected_size = 33;
> > -       } else if (bdb->version == 195) {
> > -               expected_size = 37;
> > -       } else if (bdb->version <= 197) {
> > -               expected_size = 38;
> > -       } else {
> > -               expected_size = 38;
> > -               DRM_DEBUG_DRIVER("Expected child_device_config size for BDB version %u not known; assuming %u\n",
> > -                                expected_size, bdb->version);
> > -       }
> > -
> > -       if (expected_size > sizeof(*p_child)) {
> > -               DRM_ERROR("child_device_config cannot fit in p_child\n");
> > -               return;
> > -       }
> > -
> > -       if (p_defs->child_dev_size != expected_size) {
> > -               DRM_ERROR("Size mismatch; child_device_config size=%u (expected %u); bdb->version: %u\n",
> > -                         p_defs->child_dev_size, expected_size, bdb->version);
> > +       if (p_defs->child_dev_size < sizeof(*p_child)) {
> > +               DRM_ERROR("General definiton block child device size is too small.\n");
> >                 return;
> >         }
> >         /* get the block size of general definitions */
> > @@ -1149,7 +1130,7 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
> >
> >                 child_dev_ptr = dev_priv->vbt.child_dev + count;
> >                 count++;
> > -               memcpy(child_dev_ptr, p_child, p_defs->child_dev_size);
> > +               memcpy(child_dev_ptr, p_child, sizeof(*p_child));
> >         }
> >         return;
> >  }
> > --
> > 2.1.4
> >
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel OTC
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