In commit a670ff57 ("drm/msm/dpu: always use mdp device to scale
bandwidth") we fully moved interconnect stuff to the DPU driver. This
had no change for sc7180 but _did_ have an impact for other SoCs. It
made them match the sc7180 scheme.

Unfortunately, the sc7180 scheme seems like it was a bit broken.
Specifically the interconnect needs to be on for more than just the
DPU driver's AXI bus. In the very least it also needs to be on for the
DSI driver's AXI bus. This can be seen fairly easily by doing this on
a ChromeOS sc7180-trogdor class device:

  set_power_policy --ac_screen_dim_delay=5 --ac_screen_off_delay=10
  sleep 10
  cd /sys/bus/platform/devices/ae94000.dsi/power
  echo on > control

When you do that, you'll get a warning splat in the logs about
"gcc_disp_hf_axi_clk status stuck at 'off'".

One could argue that perhaps what I have done above is "illegal" and
that it can't happen naturally in the system because in normal system
usage the DPU is pretty much always on when DSI is on. That being
said:
* In official ChromeOS builds (admittedly a 5.4 kernel with backports)
  we have seen that splat at bootup.
* Even though we don't use "autosuspend" for these components, we
  don't use the "put_sync" variants. Thus plausibly the DSI could stay
  "runtime enabled" past when the DPU is enabled. Techncially we
  shouldn't do that if the DPU's suspend ends up yanking our clock.

Let's change things such that the "bare minimum" request for the
interconnect happens in the mdss driver again. That means that all of
the children can assume that the interconnect is on at the minimum
bandwidth. We'll then let the DPU request the higher amount that it
wants.

It should be noted that this isn't as hacky of a solution as it might
initially appear. Specifically:
* Since MDSS and DPU individually get their own references to the
  interconnect then the framework will actually handle aggregating
  them. The two drivers are _not_ clobbering each other.
* When the Qualcomm interconnect driver aggregates it takes the max of
  all the peaks. Thus having MDSS request a peak, as we're doing here,
  won't actually change the total interconnect bandwidth (it won't be
  added to the request for the DPU). This perhaps explains why the
  "average" requested in MDSS was historically 0 since that one
  _would_ be added in.

NOTE also that in the downstream ChromeOS 5.4 and 5.15 kernels, we're
also seeing some RPMH hangs that are addressed by this fix. These
hangs are showing up in the field and on _some_ devices with enough
stress testing of suspend/resume. Specifically right at suspend time
with a stack crawl that looks like this (from chromeos-5.15 tree):
  rpmh_write_batch+0x19c/0x240
  qcom_icc_bcm_voter_commit+0x210/0x420
  qcom_icc_set+0x28/0x38
  apply_constraints+0x70/0xa4
  icc_set_bw+0x150/0x24c
  dpu_runtime_resume+0x50/0x1c4
  pm_generic_runtime_resume+0x30/0x44
  __genpd_runtime_resume+0x68/0x7c
  genpd_runtime_resume+0x12c/0x20c
  __rpm_callback+0x98/0x138
  rpm_callback+0x30/0x88
  rpm_resume+0x370/0x4a0
  __pm_runtime_resume+0x80/0xb0
  dpu_kms_enable_commit+0x24/0x30
  msm_atomic_commit_tail+0x12c/0x630
  commit_tail+0xac/0x150
  drm_atomic_helper_commit+0x114/0x11c
  drm_atomic_commit+0x68/0x78
  drm_atomic_helper_disable_all+0x158/0x1c8
  drm_atomic_helper_suspend+0xc0/0x1c0
  drm_mode_config_helper_suspend+0x2c/0x60
  msm_pm_prepare+0x2c/0x40
  pm_generic_prepare+0x30/0x44
  genpd_prepare+0x80/0xd0
  device_prepare+0x78/0x17c
  dpm_prepare+0xb0/0x384
  dpm_suspend_start+0x34/0xc0

We don't completely understand all the mechanisms in play, but the
hang seemed to come and go with random factors. It's not terribly
surprising that the hang is gone after this patch since the line of
code that was failing is no longer present in the kernel.

Fixes: a670ff57 ("drm/msm/dpu: always use mdp device to scale bandwidth")
Fixes: c33b7c03 ("drm/msm/dpu: add support for clk and bw scaling for display")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Tested-by: Jessica Zhang <quic_jesszhan@quicinc.com> # RB3 (sdm845) and
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/487884/
Link: https://lore.kernel.org/r/20220531160059.v2.1.Ie7f6d4bf8cce28131da31a43354727e417cae98d@changeidSigned-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>