On 11/1/2021 08:39, Jordan Justen wrote:
<John.C.Harrison@xxxxxxxxx> writes:
From: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
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?
Because the definition is nothing to do with i915. This table comes from
the hardware spec. It is not defined by the KMD and it is not currently
used by the KMD. So there is no reason for the KMD to be creating
structures for it in the same way that the KMD does not document,
define, struct, etc. every other feature of the hardware that the UMDs
might use.
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?
At the moment, the KMD does not use the table at all. We merely provide
a mechanism for the UMDs to retrieve it from the hardware.
In terms of future direction, that is something you need to take up with
the hardware architects.
The attribute ids are defined in a hardware spec.
Which spec?
Unfortunately, it is not one that is currently public. We are pushing
the relevant people to get it included in the public bspec / HRM. It is
a slow process :(.
John.
-Jordan
