On Thu, Feb 4, 2021 at 12:55 AM Benson Leung <bleung@xxxxxxxxxxxx> wrote: > > Hey Kyle, > > On Tue, Feb 2, 2021 at 8:23 AM Kyle Tso <kyletso@xxxxxxxxxx> wrote: > > > > "PD Spec Revision 3.0 Version 2.0 + ECNs 2020-12-10" introduces several > > changes regarding the ID Header VDO and the Product Type VDOs. > > > > Signed-off-by: Kyle Tso <kyletso@xxxxxxxxxx> > > We have to actually be very careful in this change, because the switch > from PD 2.0 -> PD 3.0 does not mean that a PD 3.0 DFP will never > encounter a PD 2.0 partner or cable again. > > It actually has to be the case that we may have to maintain two sets > of these object field definitions (and any other PD object decoding we > do in the kernel) and switch the decoding on pd_revision (which I > recently added here: > https://lore.kernel.org/linux-usb/20210129061406.2680146-3-bleung@xxxxxxxxxxxx). > > Just to put a point on it: PD 2.0's Passive Cable VDO has B4, which is > "Vbus through cable." PD 3.0, on the other hand, reserves this bit, so > the field is gone. We can't just delete that bit in the kernel's data > structures. We have to be able to refer to it if we encounter a PD 2.0 > cable. > > I think this change needs to be reworked so that we strictly maintain > a PD 2.0 object field definitions, and a separate PD 3.0 one too. They > will operate on the same objects, but whoever's doing the decoding has > to check the revision (2.0 vs 3.0) first to check applicability of one > set or the other. > > Thanks, > Benson > > > -- > Benson Leung > Staff Software Engineer > Chrome OS Kernel > Google Inc. > bleung@xxxxxxxxxx > Chromium OS Project > bleung@xxxxxxxxxxxx You are correct! Fix is here: https://patchwork.kernel.org/project/linux-usb/patch/20210204005036.1555294-1-kyletso@xxxxxxxxxx/ thanks, Kyle
