On Wed, Jul 24, 2019 at 3:31 PM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > [ Upstream commit c2bf1fc212f7e6f25ace1af8f0b3ac061ea48ba5 ] > > Currently Linux does not follow PCIe spec regarding the required delays > after reset. A concrete example is a Thunderbolt add-in-card that > consists of a PCIe switch and two PCIe endpoints: > > +-1b.0-[01-6b]----00.0-[02-6b]--+-00.0-[03]----00.0 TBT controller > +-01.0-[04-36]-- DS hotplug port > +-02.0-[37]----00.0 xHCI controller > \-04.0-[38-6b]-- DS hotplug port > > The root port (1b.0) and the PCIe switch downstream ports are all PCIe > gen3 so they support 8GT/s link speeds. > > We wait for the PCIe hierarchy to enter D3cold (runtime): > > pcieport 0000:00:1b.0: power state changed by ACPI to D3cold > > When it wakes up from D3cold, according to the PCIe 4.0 section 5.8 the > PCIe switch is put to reset and its power is re-applied. This means that > we must follow the rules in PCIe 4.0 section 6.6.1. > > For the PCIe gen3 ports we are dealing with here, the following applies: > > With a Downstream Port that supports Link speeds greater than 5.0 > GT/s, software must wait a minimum of 100 ms after Link training > completes before sending a Configuration Request to the device > immediately below that Port. Software can determine when Link training > completes by polling the Data Link Layer Link Active bit or by setting > up an associated interrupt (see Section 6.7.3.3). > > Translating this into the above topology we would need to do this (DLLLA > stands for Data Link Layer Link Active): > > pcieport 0000:00:1b.0: wait for 100ms after DLLLA is set before access to 0000:01:00.0 > pcieport 0000:02:00.0: wait for 100ms after DLLLA is set before access to 0000:03:00.0 > pcieport 0000:02:02.0: wait for 100ms after DLLLA is set before access to 0000:37:00.0 > > I've instrumented the kernel with additional logging so we can see the > actual delays the kernel performs: > > pcieport 0000:00:1b.0: power state changed by ACPI to D0 > pcieport 0000:00:1b.0: waiting for D3cold delay of 100 ms > pcieport 0000:00:1b.0: waking up bus > pcieport 0000:00:1b.0: waiting for D3hot delay of 10 ms > pcieport 0000:00:1b.0: restoring config space at offset 0x2c (was 0x60, writing 0x60) > ... > pcieport 0000:00:1b.0: PME# disabled > pcieport 0000:01:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:01:00.0: PME# disabled > pcieport 0000:02:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:02:00.0: PME# disabled > pcieport 0000:02:01.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:02:01.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407) > pcieport 0000:02:01.0: PME# disabled > pcieport 0000:02:02.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:02:02.0: PME# disabled > pcieport 0000:02:04.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:02:04.0: PME# disabled > pcieport 0000:02:01.0: PME# enabled > pcieport 0000:02:01.0: waiting for D3hot delay of 10 ms > pcieport 0000:02:04.0: PME# enabled > pcieport 0000:02:04.0: waiting for D3hot delay of 10 ms > thunderbolt 0000:03:00.0: restoring config space at offset 0x14 (was 0x0, writing 0x8a040000) > ... > thunderbolt 0000:03:00.0: PME# disabled > xhci_hcd 0000:37:00.0: restoring config space at offset 0x10 (was 0x0, writing 0x73f00000) > ... > xhci_hcd 0000:37:00.0: PME# disabled > > For the switch upstream port (01:00.0) we wait for 100ms but not taking > into account the DLLLA requirement. We then wait 10ms for D3hot -> D0 > transition of the root port and the two downstream hotplug ports. This > means that we deviate from what the spec requires. > > Performing the same check for system sleep (s2idle) transitions we can > see following when resuming from s2idle: > > pcieport 0000:00:1b.0: power state changed by ACPI to D0 > pcieport 0000:00:1b.0: restoring config space at offset 0x2c (was 0x60, writing 0x60) > ... > pcieport 0000:01:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > ... > pcieport 0000:02:02.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > pcieport 0000:02:02.0: restoring config space at offset 0x2c (was 0x0, writing 0x0) > pcieport 0000:02:01.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > pcieport 0000:02:04.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > pcieport 0000:02:02.0: restoring config space at offset 0x28 (was 0x0, writing 0x0) > pcieport 0000:02:00.0: restoring config space at offset 0x3c (was 0x1ff, writing 0x201ff) > pcieport 0000:02:02.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1fff1) > pcieport 0000:02:01.0: restoring config space at offset 0x2c (was 0x0, writing 0x60) > pcieport 0000:02:02.0: restoring config space at offset 0x20 (was 0x0, writing 0x73f073f0) > pcieport 0000:02:04.0: restoring config space at offset 0x2c (was 0x0, writing 0x60) > pcieport 0000:02:01.0: restoring config space at offset 0x28 (was 0x0, writing 0x60) > pcieport 0000:02:00.0: restoring config space at offset 0x2c (was 0x0, writing 0x0) > pcieport 0000:02:02.0: restoring config space at offset 0x1c (was 0x101, writing 0x1f1) > pcieport 0000:02:04.0: restoring config space at offset 0x28 (was 0x0, writing 0x60) > pcieport 0000:02:01.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1ff10001) > pcieport 0000:02:00.0: restoring config space at offset 0x28 (was 0x0, writing 0x0) > pcieport 0000:02:02.0: restoring config space at offset 0x18 (was 0x0, writing 0x373702) > pcieport 0000:02:04.0: restoring config space at offset 0x24 (was 0x10001, writing 0x49f12001) > pcieport 0000:02:01.0: restoring config space at offset 0x20 (was 0x0, writing 0x73e05c00) > pcieport 0000:02:00.0: restoring config space at offset 0x24 (was 0x10001, writing 0x1fff1) > pcieport 0000:02:04.0: restoring config space at offset 0x20 (was 0x0, writing 0x89f07400) > pcieport 0000:02:01.0: restoring config space at offset 0x1c (was 0x101, writing 0x5151) > pcieport 0000:02:00.0: restoring config space at offset 0x20 (was 0x0, writing 0x8a008a00) > pcieport 0000:02:02.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020) > pcieport 0000:02:04.0: restoring config space at offset 0x1c (was 0x101, writing 0x6161) > pcieport 0000:02:01.0: restoring config space at offset 0x18 (was 0x0, writing 0x360402) > pcieport 0000:02:00.0: restoring config space at offset 0x1c (was 0x101, writing 0x1f1) > pcieport 0000:02:04.0: restoring config space at offset 0x18 (was 0x0, writing 0x6b3802) > pcieport 0000:02:02.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407) > pcieport 0000:02:00.0: restoring config space at offset 0x18 (was 0x0, writing 0x30302) > pcieport 0000:02:01.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020) > pcieport 0000:02:04.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020) > pcieport 0000:02:00.0: restoring config space at offset 0xc (was 0x10000, writing 0x10020) > pcieport 0000:02:01.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407) > pcieport 0000:02:04.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407) > pcieport 0000:02:00.0: restoring config space at offset 0x4 (was 0x100000, writing 0x100407) > xhci_hcd 0000:37:00.0: restoring config space at offset 0x10 (was 0x0, writing 0x73f00000) > ... > thunderbolt 0000:03:00.0: restoring config space at offset 0x14 (was 0x0, writing 0x8a040000) > > This is even worse. None of the mandatory delays are performed. If this > would be S3 instead of s2idle then according to PCI FW spec 3.2 section > 4.6.8. there is a specific _DSM that allows the OS to skip the delays > but this platform does not provide the _DSM and does not go to S3 anyway > so no firmware is involved that could already handle these delays. > > In this particular Intel Coffee Lake platform these delays are not > actually needed because there is an additional delay as part of the ACPI > power resource that is used to turn on power to the hierarchy but since > that additional delay is not required by any of standards (PCIe, ACPI) > it is not present in the Intel Ice Lake, for example where missing the > mandatory delays causes pciehp to start tearing down the stack too early > (links are not yet trained). > > For this reason, change the PCIe portdrv PM resume hooks so that they > perform the mandatory delays before the downstream component gets > resumed. We perform the delays before port services are resumed because > otherwise pciehp might find that the link is not up (even if it is just > training) and tears-down the hierarchy. > We have gotten multiple reports in Fedora that this patch has broken suspend for users of 5.1.20 and 5.2 stable kernels. Justin
