On Wed, Aug 19, 2020 at 12:58:18PM -0400, Lyude Paul wrote: > On Wed, 2020-08-19 at 16:06 +0300, Mika Westerberg wrote: > > Kai-Heng Feng reported that it takes a long time (> 1 s) to resume > > Thunderbolt-connected devices from both runtime suspend and system sleep > > (s2idle). > > > > This was because some Downstream Ports that support > 5 GT/s do not also > > support Data Link Layer Link Active reporting. Per PCIe r5.0 sec 6.6.1: > > > > 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). > > > > Sec 7.5.3.6 requires such Ports to support DLL Link Active reporting, but > > at least the Intel JHL6240 Thunderbolt 3 Bridge [8086:15c0] and the Intel > > JHL7540 Thunderbolt 3 Bridge [8086:15ea] do not. > > > > Previously we tried to wait for Link training to complete, but since there > > was no DLL Link Active reporting, all we could do was wait the worst-case > > 1000 ms, then another 100 ms. > > > > Instead of using the supported speeds to determine whether to wait for Link > > training, check whether the port supports DLL Link Active reporting. The > > Ports in question do not, so we'll wait only the 100 ms required for Ports > > that support Link speeds <= 5 GT/s. > > > > This of course assumes these Ports always train the Link within 100 ms even > > if they are operating at > 5 GT/s, which is not required by the spec. > > > > This version adds a special check for devices whose power management is > > disabled by their driver (->pm_cap is set to zero). This is needed to > > avoid regression with some NVIDIA GPUs. > > Hm, I'm not entirely sure that the link training delay is specific to laptops > with ->pm_cap set to 0, I think we should try figuring out if there's any > laptops that match those characteristics before moving forward with this - I'll > take a look through the test machines I've got available today OK, thanks!
