On 1/15/20 8:18 AM, Chris Wilson wrote:
Quoting Daniele Ceraolo Spurio (2020-01-15 15:57:27)
On 1/15/2020 12:40 AM, Chris Wilson wrote:
Quoting Daniele Ceraolo Spurio (2020-01-15 01:31:36)
We currently wait until we attempt to load the GuC to confirm if we're
in GuC mode or not, at which point a lot of the engine setup has already
happened and needs to be updated for GuC submission. To allow us to get
the setup done directly into GuC mode, we need to commit to using GuC
as soon as possible.
I think this is the wrong direction; as I thought the goal was to allow
delayed loading of firmware, even going as far as allowing the system to
run a browser for the user to get the firmware first. I may be
We do indeed want to keep supporting execlists mode even as some HW
features move to the GuC to allow the user to get to the binaries, but
we don't want to switch between the 2 modes without a reboot. Switching
between the 2 modes is not a HW capability that we're committed to; the
guc->elsp transition is already not possible, while the elsp->guc one
still seems to work, but who knows for how long it will?
This series is also not really changing the commitment at the
implementation level, just making it "official" and acting based on
that. Even without these patches, if the blobs are on the system we will
attempt to get into GuC mode unless we get an allocation failure or
something similar, in which case it is extremely likely that the
fall-back to non-guc will not work either.
completely wrong about that, but imho I never want to have to build
firmware images into the kernel.
I do 100% agree with this statement, although I'm not sure how this
relates to the series. Are you planning to pull some of the engine setup
to an even earlier point?
The transition from execlists to guc could be just set-wedged; delete
old engines, build guc engines. [This should also work for guc -> guc.]
Throwing away context state is ugly, but simple enough.
As mentioned above, we can't switch between elsp and GuC modes so this
transition would have to be done before the first submission to HW. Why
not go directly in GuC mode then?
So the problem is if we can't freely switch (we can never power down the
guc, that seems unlikely?) then we can't make a decision on which mode
AFAIU it's not the GuC itself that's the issue, but some of the other
units, some of which outside the GT, that can get locked in one mode
without being resettable (like what happens for the WOPCM regs for example).
to run (and which engines to initialise) until userspace is active and
has committed to supplying or not supplying a fw image. Which puts us in
a catch-22 of wanting to register the driver with userspace before we
have finalized initialisation.
I think this is the bit I'm missing. Why do you want userspace to
directly provide the firmware instead of fetching it from /lib/firmware
like we do now? The distros should pack the correct firmware in their
linux-firmware packages and it seems reasonable to me to expect the
system to be rebooted after fetching a binary by hand. We can move the
fetch to an earlier point in time if we need the info earlier, since it
does not require the HW to be ready.
If the transition is impossible, it seems like you have no choice but to
require the fw image at initialisation. I do not understand why it has
to be that way, seems such a hindrance.
My understanding from the talk I had with the HW team when we realized
that the guc->elsp transition was broken on gen11 is that the HW expects
SW to pick a mode and stick to that. The elsp->guc transition seem to
still work, but there is no guarantee it will keep doing so in the
future and therefore it doesn't seem like a good idea to build on that.
Daniele
-Chris
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