On Thursday, November 25, 2021 8:37:28 AM CET Mika Westerberg wrote:
> If protocol tunnels are already up when the driver is loaded, for
> instance if the boot firmware implements connection manager of its own,
> runtime PM reference count of the consumer devices behind the tunnel
> might have been increased already before the device link is created but
> the supplier device runtime PM reference count is not. This leads to a
> situation where the supplier (the Thunderbolt driver) can runtime
> suspend even if it should not because the corresponding protocol tunnel
> needs to be up causing the devices to be removed from the corresponding
> native bus.
>
> Prevent this from happening by making both sides of the link runtime PM
> active briefly. The pm_runtime_put() for the consumer (PCIe
> root/downstream port, xHCI) then allows it to runtime suspend again but
> keeps the supplier runtime resumed the whole time it is runtime active.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Thanks!
> ---
> drivers/thunderbolt/acpi.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/drivers/thunderbolt/acpi.c b/drivers/thunderbolt/acpi.c
> index b67e72d5644b..7c9597a33929 100644
> --- a/drivers/thunderbolt/acpi.c
> +++ b/drivers/thunderbolt/acpi.c
> @@ -7,6 +7,7 @@
> */
>
> #include <linux/acpi.h>
> +#include <linux/pm_runtime.h>
>
> #include "tb.h"
>
> @@ -74,8 +75,18 @@ static acpi_status tb_acpi_add_link(acpi_handle handle, u32 level, void *data,
> pci_pcie_type(pdev) == PCI_EXP_TYPE_DOWNSTREAM))) {
> const struct device_link *link;
>
> + /*
> + * Make them both active first to make sure the NHI does
> + * not runtime suspend before the consumer. The
> + * pm_runtime_put() below then allows the consumer to
> + * runtime suspend again (which then allows NHI runtime
> + * suspend too now that the device link is established).
> + */
> + pm_runtime_get_sync(&pdev->dev);
> +
> link = device_link_add(&pdev->dev, &nhi->pdev->dev,
> DL_FLAG_AUTOREMOVE_SUPPLIER |
> + DL_FLAG_RPM_ACTIVE |
> DL_FLAG_PM_RUNTIME);
> if (link) {
> dev_dbg(&nhi->pdev->dev, "created link from %s\n",
> @@ -84,6 +95,8 @@ static acpi_status tb_acpi_add_link(acpi_handle handle, u32 level, void *data,
> dev_warn(&nhi->pdev->dev, "device link creation from %s failed\n",
> dev_name(&pdev->dev));
> }
> +
> + pm_runtime_put(&pdev->dev);
> }
>
> out_put:
>
