On 3/20/19 6:14 AM, Lukas Wunner wrote:
>
> [EXTERNAL EMAIL]
>
> When booting a MacBookPro9,1, duplicate link downtraining messages are
> logged for the devices directly attached to the two CPU-internal Root
> Ports of the Core i7 3615QM: Once on device enumeration and once on
> enablement of the bandwidth notification interrupt on the Root Ports.
>
> Duplicate messages do not occur with Root Ports on the PCH and Downstream
> Ports on the Thunderbolt controller: Only a single message is logged for
> these, namely on device enumeration.
>
> The reason for the duplicate messages is a stale interrupt in the Link
> Status register of the 3615QM's internal Root Ports. Avoid by clearing
> the interrupt before enabling it.
>
> An alternative approach would be to clear the interrupt already on device
> enumeration or to report link downtraining only if the speed has changed.
> That way, link downtraining occurring between device enumeration and
> enablement of the bandwidth notification interrupt could be catched.
> However clearing stale interrupts before enabling them is a standard
> operating procedure for any driver and keeping the two steps in one place
> makes the code easier to follow.
>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Reviewed-by: Alexandru Gagniuc <alex.gagniuc@xxxxxxxxxxxx>
> ---
> drivers/pci/pcie/bw_notification.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/pci/pcie/bw_notification.c b/drivers/pci/pcie/bw_notification.c
> index 001d6253ad48..69e6ba2558bf 100644
> --- a/drivers/pci/pcie/bw_notification.c
> +++ b/drivers/pci/pcie/bw_notification.c
> @@ -30,6 +30,8 @@ static void pcie_enable_link_bandwidth_notification(struct pci_dev *dev)
> {
> u16 lnk_ctl;
>
> + pcie_capability_write_word(dev, PCI_EXP_LNKSTA, PCI_EXP_LNKSTA_LBMS);
> +
> pcie_capability_read_word(dev, PCI_EXP_LNKCTL, &lnk_ctl);
> lnk_ctl |= PCI_EXP_LNKCTL_LBMIE;
> pcie_capability_write_word(dev, PCI_EXP_LNKCTL, lnk_ctl);
>
