Quoting Anshuman Gupta (2022-09-14 19:13:29)
> 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)
>
> Both DG1/DG2 have a hardware bug that violates the PCIe specs
> and support 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 becomes visible 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 bind with pcieport driver.
> which really disables the PCIe poer power savings and leaves the bridge
> at D0 state.
>
> 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.
>
> V2:
> - Keep a smaller FIXME code comment for both DG1/DG2.
I think we should also have Fixes: tags to cover both platforms.
Regards, Joonas
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> Signed-off-by: Anshuman Gupta <anshuman.gupta@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_pci.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_pci.c b/drivers/gpu/drm/i915/i915_pci.c
> index 77e7df21f539..4a7d226b074f 100644
> --- a/drivers/gpu/drm/i915/i915_pci.c
> +++ b/drivers/gpu/drm/i915/i915_pci.c
> @@ -931,6 +931,14 @@ 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.
> + * 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 +1084,13 @@ 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),
> + /*
> + * 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.
> + * Let's disable i915 rpm till we fix all known issue with lmem access in D3.
> + */
> + .has_runtime_pm = 0,
> .require_force_probe = 1,
> };
>
> --
> 2.26.2
>
