在 2022-05-19星期四的 23:54 +0300，Evgeny Boger写道： > Hi qianfan, > > As Allwinner A40i user, let me first thank you for your effort for > making better upstream support for R40! > > However, I would strongly suggest *not* to add USB support to one > more > Allwinner SoC in this particular way. > The problem is, this approach consists of a number of carefully > crafted > hacks in device tree to make current drivers work on Allwinner > hardware > without modification to the drivers. > > a few examples: > > 1) please notice how ohci0 and ehci0 nodes do not contain reference > to > usb phy. It is done intentionally, otherwise EHCI will reset musb > mode. > Of course omitting phy reference here is also completely breaking > power > cycling in case of usb error and otherwise messes with a power > management. > > 2) one must always enable ohci, ehci and usb_otg nodes at the same > time. > If one forgets to enable ohci/ehci nodes while enabling usb_otg node, > the system will silently fail to work as USB host. > > 3) For host-only mode we still have to enable usb_otg node despite no > role switching is needed. That's because phy reference is missing in > ehci/ohci, so the ehci/ohci driver won't enable the PHY. > Also I might be wrong, but I think phy won't be routed to ehci/ohci > controllers is this case. > > 4) musb host controller is initialized and present to hardware though > never actually used > > To summarize, not only the resulting device tree is not describing > the > hardware properly, it is creating device tree configuration which > will > be very hard to support in future, once proper driver support is in > place. > > > At Wiren Board kernel tree we tried to untangle this issue [1-6]. > Unfortunately I didn't have time to prepare it for kernel submission > yet, but I think I better submit it as RFC to get a feedback from you > and others. Please cc me in the following patches because it's me who makes the whole dual route thing hacky. > > > [1] > https://github.com/wirenboard/linux/commit/359abbbd86ddff4d3c61179c882c286de32bb089 > [2] > https://github.com/wirenboard/linux/commit/6327f9d7972c21b229fb83457fdde643b31553f9 > [3] > https://github.com/wirenboard/linux/commit/f01f4c66758bde460a4d8c5b54ecee3b585c0232 > [4] > https://github.com/wirenboard/linux/commit/c27598ad601e5a46f624b73412a531d6f1f63d37 > [5] > https://github.com/wirenboard/linux/commit/5796d6eebb86b32a3751b2038b63af46f94954b3 > [6] > https://github.com/wirenboard/linux/commit/0928a675d875f9c2849fd3a9888f718bbb673bda > >
