[Intel-gfx] [PATCH] drm/i915/DG{1, 2}: FIXME Temporary hammer to disable rpm

[Anshuman Gupta <anshuman.gupta@intel.com>]

DG1 and DG2 has lmem, and cpu can access the lmem objects
via mmap and i915 internal i915_gem_object_pin_map() for
i915 own usages. Both of these methods has pre-requisite
requirement to keep GFX PCI endpoint in D0 for a supported
iomem transaction over PCI link. (Refer PCIe specs 5.3.1.4.1)

TODO:
With respect to i915_gem_object_pin_map(), every caller
has to grab a wakeref if gem object lies in lmem.

Till we fix all issues related to runtime PM, we need
to keep runtime PM disable on both DG1 and DG2.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
---
 drivers/gpu/drm/i915/i915_pci.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
index 77e7df21f539..f31d7f5399cc 100644
--- a/drivers/gpu/drm/i915/i915_pci.c
+++ b/drivers/gpu/drm/i915/i915_pci.c
@@ -931,6 +931,26 @@ static const struct intel_device_info dg1_info = {
 		BIT(VCS0) | BIT(VCS2),
 	/* Wa_16011227922 */
 	.__runtime.ppgtt_size = 47,
+
+	/*
+	 *  FIXME: Temporary hammer to disable rpm.
+	 *  As per PCIe specs 5.3.1.4.1, all iomem read write request over a PCIe
+	 *  function will be unsupported in case PCIe endpoint function is in D3.
+	 *  But both DG1/DG2 has a hardware bug that violates the PCIe specs
+	 *  and supports the iomem read write transaction over PCIe bus despite
+	 *  endpoint is D3 state.
+	 *  Due to above H/W bug, we had never observed any issue with i915 runtime
+	 *  PM versus lmem access.
+	 *  But this issue gets discover when PCIe gfx endpoint's upstream
+	 *  bridge enters to D3, at this point any lmem read/write access will be
+	 *  returned as unsupported request. But again this issue is not observed
+	 *  on every platform because it has been observed on few host machines
+	 *  DG1/DG2 endpoint's upstream bridge does not binds with pcieport driver.
+	 *  which really disables the PCIe power savings and leaves the bridge to D0
+	 *  state.
+	 *  Let's disable i915 rpm till we fix all known issue with lmem access in D3.
+	 */
+	.has_runtime_pm = 0,
 };
 
 static const struct intel_device_info adl_s_info = {
@@ -1076,6 +1096,7 @@ static const struct intel_device_info dg2_info = {
 	XE_LPD_FEATURES,
 	.__runtime.cpu_transcoder_mask = BIT(TRANSCODER_A) | BIT(TRANSCODER_B) |
 			       BIT(TRANSCODER_C) | BIT(TRANSCODER_D),
+	.has_runtime_pm = 0,
 	.require_force_probe = 1,
 };
 
-- 
2.26.2