Hi Matt,
On Thu, Oct 19, 2023 at 10:02:42AM -0700, Matt Roper wrote:
> The steering control and semaphore registers are inside an "always on"
> power domain with respect to RC6. However there are some issues if
> higher-level platform sleep states are entering/exiting at the same time
> these registers are accessed. Grabbing GT forcewake and holding it over
> the entire lock/steer/unlock cycle ensures that those sleep states have
> been fully exited before we access these registers.
>
> This is expected to become a formally documented/numbered workaround
> soon.
>
> Note that this patch alone isn't expected to have an immediately
> noticeable impact on MCR (mis)behavior; an upcoming pcode firmware
> update will also be necessary to provide the other half of this
> workaround.
right... I did try this, but so fare we hold the forcewake when
calling mcr_lock().
> v2:
> - Move the forcewake inside the Xe_LPG-specific IP version check. This
> should only be necessary on platforms that have a steering semaphore.
>
> Fixes: 4186e2185b4f ("drm/i915/gt: Add dedicated MCR lock")
Is this the right Fixes tag? This is adding the spinlock around
MCR, but the power domain needs to be taken independently from
the lock... I think the right fix here is
Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
Cc: <stable@xxxxxxxxxxxxxxx> # v6.3+
When the access to the hardware was added.
BTW, given that currently we hold the forcewake already, is this
really a fix or is this more looking at the future? Is the Fixes
tag necessary?
> Cc: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
> Cc: Jonathan Cavitt <jonathan.cavitt@xxxxxxxxx>
> Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
In any case,
Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Andi
