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Wysocki" Subject: RE: [PATCH v4] PCI / ACPI: Assume `HotPlugSupportInD3` only if device can wake from D3 Thread-Topic: [PATCH v4] PCI / ACPI: Assume `HotPlugSupportInD3` only if device can wake from D3 Thread-Index: AQHYOIH4cjkXql1VyUKxzqcCT79LiazApEsAgAAAXoCADIi5gIAAUUqAgAAEXdCAAAnIgIAAAD8g Date: Wed, 23 Mar 2022 21:51:18 +0000 Message-ID: References: <20220323214239.GA1373960@bhelgaas> In-Reply-To: <20220323214239.GA1373960@bhelgaas> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_Enabled=true; MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_SetDate=2022-03-23T21:43:38Z; MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_Method=Privileged; MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_Name=Public-AIP 2.0; MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_SiteId=3dd8961f-e488-4e60-8e11-a82d994e183d; MSIP_Label_d4243a53-6221-4f75-8154-e4b33a5707a1_ActionId=89d0f93e-ccc2-4607-829b-67810c99a68f; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BL1PR12MB5157.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 0c3ebb5d-7036-4180-0746-08da0d1742e2 X-MS-Exchange-CrossTenant-originalarrivaltime: 23 Mar 2022 21:51:18.2614 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: zCVlqSTyRxv75J1XuXXtPs1gsASQBHAyRZX7BrC3lC67W0nXS9xWwRduE1qgFGQvuPsF2/wJDzBx7JhaYmXkSg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4975 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org [Public] > -----Original Message----- > From: Bjorn Helgaas > Sent: Wednesday, March 23, 2022 16:43 > To: Limonciello, Mario > Cc: Bjorn Helgaas ; open list:PCI SUBSYSTEM pci@vger.kernel.org>; Linux PM ; Mehta, Sanju > ; Rafael J. Wysocki > Subject: Re: [PATCH v4] PCI / ACPI: Assume `HotPlugSupportInD3` only if d= evice > can wake from D3 >=20 > On Wed, Mar 23, 2022 at 09:26:15PM +0000, Limonciello, Mario wrote: > > [Public] > > > > > > > > On Wed, Mar 23, 2022 at 11:01:05AM -0500, Mario Limonciello wrote: > > > > On 3/15/22 11:36, Rafael J. Wysocki wrote: > > > > > On Tue, Mar 15, 2022 at 5:35 PM Rafael J. Wysocki > > > wrote: > > > > > > > > > > > > On Tue, Mar 15, 2022 at 4:33 PM Mario Limonciello > > > > > > wrote: > > > > > > > > > > > > > > According to the Microsoft spec the _DSD `HotPlugSupportInD3`= is > > > > > > > indicates the ability for a bridge to be able to wakeup from = D3: > > > > > > > > > > > > > > This ACPI object [HotPlugSupportInD3] enables the operatin= g > system > > > > > > > to identify and power manage PCIe Root Ports that are capa= ble of > > > > > > > handling hot plug events while in D3 state. > > > > > > > > > > > > > > This however is static information in the ACPI table at BIOS > compilation > > > > > > > time and on some platforms it's possible to configure the fir= mware at > > > boot > > > > > > > up such that _S0W returns "0" indicating the inability to wak= e up the > > > > > > > device from D3 as explained in the ACPI specification: > > > > > > > > > > > > > > 7.3.20 _S0W (S0 Device Wake State) > > > > > > > > > > > > > > This object evaluates to an integer that conveys to OSPM t= he > deepest > > > > > > > D-state supported by this device in the S0 system sleeping= state > > > > > > > where the device can wake itself. > > > > > > > > > > > > > > This mismatch may lead to being unable to enumerate devices b= ehind > the > > > > > > > hotplug bridge when a device is plugged in. To remedy these > situations > > > > > > > that `HotPlugSupportInD3` is specified by _S0W returns 0, exp= licitly > > > > > > > check that the ACPI companion has returned _S0W greater than = or > equal > > > > > > > to 3 and the device has a GPE allowing the device to generate= wakeup > > > > > > > signals handled by the platform in `acpi_pci_bridge_d3`. > > > > > > > > > > > > > > Windows 10 and Windows 11 both will prevent the bridge from g= oing > in > > > D3 > > > > > > > when the firmware is configured this way and this changes ali= gns the > > > > > > > handling of the situation to be the same. > > > > > > > > > > > > > > Link: > > > > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fuefi.= org > %2F&data=3D04%7C01%7CMario.Limonciello%40amd.com%7C095e9cb1cb3 > 34458a08d08da0d1610bf%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0 > %7C637836685684066439%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata > =3DaAj91EajV77J7GjWEGGhAYLAb9Al2TMsH1baasdVdyI%3D&reserved=3D0 > > > > %2Fhtmlspecs%2FACPI_Spec_6_4_html%2F07_Power_and_Performance_Mgmt > > > %2Fdevice-power-management-objects.html%3Fhighlight%3Ds0w%23s0w- > s0- > > > device-wake- > > > > state&data=3D04%7C01%7Cmario.limonciello%40amd.com%7C1f96c7aa37a > > > > c47640d6208da0d0efd67%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0 > > > > %7C637836655281536690%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > > > > MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata > > > > =3DCw1OTYiX9BD3gh8eN3Zyz6%2FK8YFgqbn6bgi9%2FjNsnrM%3D&reserved > > > =3D0 > > > > > > > Link: > > > > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fdocs.= mi > %2F&data=3D04%7C01%7CMario.Limonciello%40amd.com%7C095e9cb1cb3 > 34458a08d08da0d1610bf%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0 > %7C637836685684066439%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > MDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata > =3Dv8YYoxTCp1drb7ZxgbDkrgA2Nc3TxbENLBfPxbo1CTI%3D&reserved=3D0 > > > crosoft.com%2Fen-us%2Fwindows-hardware%2Fdrivers%2Fpci%2Fdsd-for- > pcie- > > > root-ports%23identifying-pcie-root-ports-supporting-hot-plug-in- > > > > d3&data=3D04%7C01%7Cmario.limonciello%40amd.com%7C1f96c7aa37ac4 > > > > 7640d6208da0d0efd67%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0% > > > > 7C637836655281536690%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > > DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=3D > > > > UkB5lmz1QBUzWVM6%2BuNzJsleP%2Fi%2BDCJJuSgINiNbymo%3D&reserv > > > ed=3D0 > > > > > > > Fixes: 26ad34d510a87 ("PCI / ACPI: Whitelist D3 for more PCIe > hotplug > > > ports") > > > > > > > Signed-off-by: Mario Limonciello > > > > > > > > > > > > No more comments from me: > > > > > > > > > > > > Reviewed-by: Rafael J. Wysocki > > > > > > > > > > Or please let me know if I should pick it up. > > > > > > > > Bjorn, > > > > > > > > Friendly reminder on this one. > > > > > > Thanks; we're in the middle of the merge window now, so I'll wait til= l > > > that's over unless this is an emergency. > > > > Actually it's a pretty important problem. We waffled on the nuts and > > bolts of this commit during the 5.17 RC's, but I didn't think we would > > make it out to the merge window before it got picked. I guess I should > > have spoke up on the urgency earlier. > > > > > IIUC the bug this fixes is that "when a bridge is in D3cold, we don't > > > notice when a device is hot-added below it," right? So we need to > > > avoid putting the bridge in D3cold? > > > > When the ASL has been configured this way (to return 0 for _S0W) the > > lower level hardware implementation will lead to hotplugged devices > > not being detected. > > Without this commit the hardware will expect to be in D0, but the kerne= l > > will select D3hot. So yes; the outcome is that hotplugged PCIe devices > > don't work. > > > > > Is there a typical scenario where this bites users? I don't think we > > > ever saw an actual problem report? > > > > This is the common way that these systems are being shipped. I have > > plenty of private reports related to this, but nothing public to link t= o. >=20 > I still have no clue how many people this affects, what kernel > versions, etc. If there are no public reports, it suggests that it > doesn't affect distro kernels or production machines yet. >=20 > Can we at least list some common scenarios? E.g., it affects kernels > after commit X, or it affects machines with CPUs newer than Y, or it > affects a certain kind of tunneling, etc? Distros need this > information so they can figure whether and how far to backport things > like this. It's going to affect any retail machine with the SOC we refer to in the ker= nel as "Yellow Carp". This is one of the first non-Intel USB4 hosts and will b= e using the USB4 SW CM in the kernel. Without this change, effectively PCIe tunneling will not work when any down= stream PCIe device is hotplugged. In the right circumstances it might work if it's coldbooted (if the paths s= elected by the pre-boot firmware connection manager are identical to that selected by SW CM). Yellow carp isn't supported in the kernel until 5.14, so should this be bac= kported it shouldn't need to go any further than 5.14. (Realistically though no di= stro should be on 5.14, they should have gone to the 5.15 LTS). =20 Should it behave well baking in mainline, I would also later suggest to bri= ng it back to 5.15.y and later as well for distros to pickup. >=20 > > FYI: the earlier version of this was: > > > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fpatch= w > ork.kernel.org%2Fproject%2Flinux-usb%2Fpatch%2F1646658319-59532-1-git- > send-email- > Sanju.Mehta%40amd.com%2F&data=3D04%7C01%7CMario.Limonciello%40a > md.com%7C095e9cb1cb334458a08d08da0d1610bf%7C3dd8961fe4884e608e11 > a82d994e183d%7C0%7C0%7C637836685684066439%7CUnknown%7CTWFpbGZ > sb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0 > %3D%7C3000&sdata=3DtMSmfEl2%2FcvcFwNr7tg8QBi3s6HA8ZBgg5rCa7DZD > Hg%3D&reserved=3D0 > > This is basically to intentionally pull the device out of D3hot when a > > tunnel is created.