Re: [Intel-gfx] [PATCH v2 2/2] drm/i915/uapi: Add query for hwconfig table

[Jordan Justen <jordan.l.justen@intel.com>]

<John.C.Harrison@Intel.com> writes:

> From: Rodrigo Vivi <rodrigo.vivi@intel.com>
>
> GuC contains a consolidated table with a bunch of information about the
> current device.
>
> Previously, this information was spread and hardcoded to all the components
> including GuC, i915 and various UMDs. The goal here is to consolidate
> the data into GuC in a way that all interested components can grab the
> very latest and synchronized information using a simple query.
>
> As per most of the other queries, this one can be called twice.
> Once with item.length=0 to determine the exact buffer size, then
> allocate the user memory and call it again for to retrieve the
> table data. For example:
>   struct drm_i915_query_item item = {
>     .query_id = DRM_I915_QUERY_HWCONCFIG_TABLE;
>   };
>   query.items_ptr = (int64_t) &item;
>   query.num_items = 1;
>
>   ioctl(fd, DRM_IOCTL_I915_QUERY, query, sizeof(query));
>
>   if (item.length <= 0)
>     return -ENOENT;
>
>   data = malloc(item.length);
>   item.data_ptr = (int64_t) &data;
>   ioctl(fd, DRM_IOCTL_I915_QUERY, query, sizeof(query));
>
>   // Parse the data as appropriate...
>
> The returned array is a simple and flexible KLV (Key/Length/Value)
> formatted table. For example, it could be just:
>   enum device_attr {
>      ATTR_SOME_VALUE = 0,
>      ATTR_SOME_MASK  = 1,
>   };
>
>   static const u32 hwconfig[] = {
>       ATTR_SOME_VALUE,
>       1,             // Value Length in DWords
>       8,             // Value
>
>       ATTR_SOME_MASK,
>       3,
>       0x00FFFFFFFF, 0xFFFFFFFF, 0xFF000000,
>   };

Seems simple enough, so why doesn't i915 define the format of the
returned hwconfig blob in i915_drm.h?

struct drm_i915_hwconfig {
	uint32_t key;
	uint32_t length;
	uint32_t values[];
};

It sounds like the kernel depends on the closed source guc being loaded
to return this information. Is that right? Will i915 also become
dependent on some of this data such that it won't be able to initialize
without the firmware being loaded?

> The attribute ids are defined in a hardware spec.

Which spec?

-Jordan