Re: My AlderLake Dell (XPS-9320) needs these patches to get full standby/low-power modes

[Kenneth Crudup <kenny@panix.com>]

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OK, it looks like the effective change (that's not already contained in 
the LTR SNOOP patches already in Linus' master (et al.)) comes from this 
line from the Ubuntu commit 1a0102a0 ("UBUNTU: SAUCE: PCI/ASPM: Enable 
ASPM for links under VMD domain"):

----
diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 00143f5fb83a..d2ff44e7fbb1 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -688,7 +688,8 @@ static void pcie_aspm_cap_init(struct 
pcie_link_state *link, int blacklist)
         aspm_l1ss_init(link);

         /* Save default state */
-       link->aspm_default = link->aspm_enabled;
+       link->aspm_default = parent->dev_flags & PCI_DEV_FLAGS_ENABLE_ASPM ?
+                            ASPM_STATE_ALL : link->aspm_enabled;
----

Where "PCI_DEV_FLAGS_ENABLE_ASPM" (a new flag) is set if the parent 
bridge is a VMD (determined via Ubuntu commit 154d48da2 ("UBUNTU: SAUCE: 
vmd: fixup bridge ASPM by driver name instead").

So, as we've both noticed, most of the three patches I'd pointed out 
aren't required as the LTR SNOOP values are either fixed up, or 
previously set in the BIOS.

So I've folded the new commits into the attached patch (against Linus' 
master), which now gives me full power-saving.

-K


On 12/13/24 12:27, Kenneth Crudup wrote:
> 
> Turns out that my current VMD is already listed as "VMD_FEATS_CLIENT" 
> after all:
> 
> ----
>          {PCI_VDEVICE(INTEL, 0x467f),
>                  .driver_data = VMD_FEATS_CLIENT,},
> ----
> 0000:00:0e.0 0104: 8086:467f
>          Subsystem: 1028:0af3
>          Flags: bus master, fast devsel, latency 0, IOMMU group 9
>          Memory at 603c000000 (64-bit, non-prefetchable) [size=32M]
>          Memory at 72000000 (32-bit, non-prefetchable) [size=32M]
>          Memory at 6040100000 (64-bit, non-prefetchable) [size=1M]
>          Capabilities: [80] MSI-X: Enable+ Count=19 Masked-
>          Capabilities: [90] Express Root Complex Integrated Endpoint, 
> MSI 00
>          Capabilities: [e0] Power Management version 3
>          Kernel driver in use: vmd
> ----
> 
> I'm going to compare the commits you'd pointed out in master to what the 
> working (Ubuntu) patches do and figure out where the disconnect is.
> 
> -K
> 
> On 12/13/24 11:48, Kenneth Crudup wrote:
>>
>> I was really hopeful this would have handled it, but no joy.
>>
>> I also tried dropping "PCI/ASPM: Enable LTR for endpoints behind VMD" 
>> and "PCI/ASPM: Enable ASPM for links under VMD domain" each separately 
>> on top of the below quirk patch to no avail.
>>
>> The only thing that works is the aggregate patch I've added.
>>
>>  > However, IDs 0x9a09, 0xa0b0, and 0xa0bc are NOT tagged with
>>  > VMD_FEATS_CLIENT.  In fact, they're not included in vmd_ids[] at all,
>>  > so I'd be surprised if VMD worked for those devices unless BIOS set
>>  > up the VMD itself.
>>
>> Yeah, my BIOS does- not sure if you'd missed it, but I'd rewritten 
>> "Enable LTR for endpoints behind VMD" to print if the BIOS already 
>> does that for you, and sent the patch here (since I wasn't seeing the 
>> message printed when the fixup was being done and wanted to know why).
>>
>> I'd REALLY like to get this into mainline, so if there's anything I 
>> can do to help, LMK.
>>
>> Thanks,
>> -Kenny
>>
>>
>> On 12/13/24 08:43, Bjorn Helgaas wrote:
>>> [+cc David, Nirmal, linux-pci]
>>>
>>> On Thu, Dec 12, 2024 at 03:04:53PM -0800, Kenneth Crudup wrote:
>>>> On 12/12/24 12:56, Bjorn Helgaas wrote:
>>>>> On Wed, Dec 11, 2024 at 03:26:37PM -0800, Kenneth Crudup wrote:
>>>>>> So we're on 6.13-rc2 and the patches are getting closer and
>>>>>> closer, but they still need to be manually added.
>>>>>>
>>>>>> The good news is now only (variants of) "PCI/ASPM: Enable LTR
>>>>>> for endpoints behind VMD" and "PCI/ASPM: Enable ASPM for links
>>>>>> under VMD domain" are needed.
>>>> ...
>>>
>>>> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/ 
>>>> lunar/commit/?id=47c7bfd31514e7b54a1f830f7707297aebbb8679
>>>
>>> This is "UBUNTU: SAUCE: PCI/ASPM: Enable LTR for endpoints behind
>>> VMD", which writes PCI_LTR_MAX_SNOOP_LAT and PCI_LTR_MAX_NOSNOOP_LAT
>>> for PCI_CLASS_STORAGE_EXPRESS devices directly below VMDs with Device
>>> IDs 0x9a09, 0xa0b0, or 0xa0bc.
>>>
>>> This looks equivalent in spirit to upstream
>>> https://git.kernel.org/linus/f492edb40b54 ("PCI: vmd: Add quirk to
>>> configure PCIe ASPM and LTR"), which writes PCI_LTR_MAX_SNOOP_LAT and
>>> PCI_LTR_MAX_NOSNOOP_LAT for any kind of device below VMDs tagged with
>>> VMD_FEATS_CLIENT, which includes 0x467f, 0x4c3d, 0x7d0b, 0x9a0b,
>>> 0xa77f, 0xad0b, 0xb06f, 0xb60b.
>>>
>>> However, IDs 0x9a09, 0xa0b0, and 0xa0bc are NOT tagged with
>>> VMD_FEATS_CLIENT.  In fact, they're not included in vmd_ids[] at all,
>>> so I'd be surprised if VMD worked for those devices unless BIOS set
>>> up the VMD itself.
>>>
>>> Maybe David or Nirmal can comment on this?
>>>
>>>> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/ 
>>>> lunar/commit/?id=1a0102a08f206149d9abd56c2b28877c878b5526
>>>
>>> This is "UBUNTU: SAUCE: PCI/ASPM: Enable ASPM for links under VMD
>>> domain", which adds "link->aspm_default = ASPM_STATE_ALL" for device
>>> IDs 0x9a09 and 0xa0b0.
>>>
>>> This looks like it should also be handled by upstream f492edb40b54
>>> ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR") [1], which adds
>>> "pci_enable_link_state(pdev, PCIE_LINK_STATE_ALL)".
>>>
>>> But again, the Device IDs mentioned in the Ubuntu commit are NOT
>>> included in the upstream VMD_FEATS_CLIENT list.
>>>
>>>> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/ 
>>>> lunar/commit/?id=154d48da2c57514e4b5dadc7b8c70a4edb550981
>>>
>>> This is "UBUNTU: SAUCE: vmd: fixup bridge ASPM by driver name
>>> instead", which applies the quirk that writes PCI_LTR_MAX_SNOOP_LAT
>>> and PCI_LTR_MAX_NOSNOOP_LAT for PCI_CLASS_STORAGE_EXPRESS devices
>>> below any VMD claimed by the "vmd" driver, not just VMDs with Device
>>> IDs 0x9a09, 0xa0b0, or 0xa0bc.
>>>
>>> I think the only thing that's missing is that the upstream vmd_ids[]
>>> needs to be updated with some new VMD Device IDs that are tagged with
>>> VMD_FEATS_CLIENT.
>>>
>>> I don't know what the vmd_ids[] strategy is, but Kenneth, you might
>>> try an upstream patch like the one below.  If that resolves the
>>> standby/low-power issues, maybe David or Nirmal can figure out the
>>> "right" way to do this.
>>>
>>> Bjorn
>>>
>>> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
>>> index 9d9596947350..4de7ff3bbf23 100644
>>> --- a/drivers/pci/controller/vmd.c
>>> +++ b/drivers/pci/controller/vmd.c
>>> @@ -1109,6 +1109,12 @@ static const struct pci_device_id vmd_ids[] = {
>>>                   .driver_data = VMD_FEATS_CLIENT,},
>>>       {PCI_VDEVICE(INTEL, 0xb06f),
>>>                   .driver_data = VMD_FEATS_CLIENT,},
>>> +    {PCI_VDEVICE(INTEL, 0x9a09),
>>> +                .driver_data = VMD_FEATS_CLIENT,},
>>> +    {PCI_VDEVICE(INTEL, 0xa0b0),
>>> +                .driver_data = VMD_FEATS_CLIENT,},
>>> +    {PCI_VDEVICE(INTEL, 0xa0bc),
>>> +                .driver_data = VMD_FEATS_CLIENT,},
>>>       {0,}
>>>   };
>>>   MODULE_DEVICE_TABLE(pci, vmd_ids);
>>>
>>
> 

-- 
Kenneth R. Crudup / Sr. SW Engineer, Scott County Consulting, Orange 
County CA

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diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 28567d457613..a5df6230cf3c 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -768,6 +768,31 @@ static void aspm_l1ss_init(struct pcie_link_state *link)
 		aspm_calc_l12_info(link, parent_l1ss_cap, child_l1ss_cap);
 }
 
+/*
+ * BIOS may not be able to access config space of devices under VMD domain, so
+ * it relies on software to enable ASPM for links under VMD.
+ */
+static bool pci_fixup_vmd_bridge_enable_aspm(struct pci_dev *pdev)
+{
+       struct pci_bus *bus = pdev->bus;
+       struct device *dev;
+       struct pci_driver *pdrv;
+
+       if (!pci_is_root_bus(bus))
+               return false;
+
+       dev = bus->bridge->parent;
+       if (dev == NULL)
+               return false;
+
+       pdrv = pci_dev_driver(to_pci_dev(dev));
+       if (pdrv == NULL || strcmp("vmd", pdrv->name))
+               return false;
+
+       pci_info(pdev, "enable ASPM for pci bridge behind vmd");
+       return true;
+}
+
 static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 {
 	struct pci_dev *child = link->downstream, *parent = link->pdev;
@@ -846,7 +871,8 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 	}
 
 	/* Save default state */
-	link->aspm_default = link->aspm_enabled;
+	link->aspm_default = pci_fixup_vmd_bridge_enable_aspm(parent) ?
+		PCIE_LINK_STATE_ASPM_ALL : link->aspm_enabled;
 
 	/* Setup initial capable state. Will be updated later */
 	link->aspm_capable = link->aspm_support;