[Intel-gfx] [PATCH 1/2 v2 addendum] drm/i915: Allow parsing of variable size child device entries from VBT

[Jani Nikula]

On Thu, 13 Aug 2015, David Weinehall <david.weinehall at linux.intel.com> wrote:
> On Wed, Aug 12, 2015 at 03:13:35PM +0300, Jani Nikula wrote:
>> On Wed, 12 Aug 2015, David Weinehall <david.weinehall at linux.intel.com> wrote:
>> > Some more fixup is needed; the bits from Antti's patch
>> > that actually expanded the struct to fully fit the newer
>> > versions of the child_device_config was part of the second
>> > patch; since that patch hasn't been merged yet we need this bit:
>> >
>> > This applies on top of the patch you already merged
>> > (the Iboost patch will need corresponding adjustment to
>> >  remove the changes I split out):
>> >
>> > Expand common_child_dev_config to be able to fit all information
>> > defined by the latest VBT specification.
>> >
>> > Signed-off-by: David Weinehall <david.weinehall at linux.intel.com>
>> > CC: Antti Koskipaa <antti.koskipaa at linux.intel.com>
>> > ---
>> >  intel_bios.c |    7 ++++++-
>> >  intel_bios.h |    4 ++++
>> >  2 files changed, 10 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
>> > index 990acc20771a..40e2cc4e7419 100644
>> > --- a/drivers/gpu/drm/i915/intel_bios.c
>> > +++ b/drivers/gpu/drm/i915/intel_bios.c
>> > @@ -1038,6 +1038,10 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
>> >  		DRM_DEBUG_KMS("No general definition block is found, no devices defined.\n");
>> >  		return;
>> >  	}
>> > +	/* Remember to keep this in sync with child_device_config;
>> > +	 * whenever a new feature is added to BDB that causes that
>> > +	 * struct to grow this needs to be updated too
>> > +	 */
>> 
>> BUILD_BUG_ON(something about sizeof child device config) ?
>
> The idea is nice, but...  We get the size to copy (expected_size)
> from the version-switch statement (so it's not available during build);
> thus we cannot know at compile time whether expected_size is larger than
> sizeof(child_device_config).
>
> This is yet another argument in favour of a version:feature
> table I think; that would allow for compile-time validation.
>
> Unless someone else volunteers to refactor this code I can dig in once
> I get back from vacation.

Right. To be clear, my question should not block this from being merged.

BR,
Jani

>
>
> Kind regards, David

-- 
Jani Nikula, Intel Open Source Technology Center