Re: [PATCH RFC 0/5] Introduced new Cadence USBSSP DRD Driver.

Peter Chen
2020-06-29T03:41:56Z

On 20-06-26 07:19:56, Pawel Laszczak wrote:
> Hi Felipe,
>
> >
> >Hi,
> >
> >Pawel Laszczak <pawell@cadence.com> writes:
> >> This patch introduce new Cadence USBSS DRD driver to linux kernel.
> >>
> >> The Cadence USBSS DRD Controller is a highly configurable IP Core which
> >> can be instantiated as Dual-Role Device (DRD), Peripheral Only and
> >> Host Only (XHCI)configurations.
> >>
> >> The current driver has been validated with FPGA burned. We have support
> >> for PCIe bus, which is used on FPGA prototyping.
> >>
> >> The host side of USBSS-DRD controller is compliance with XHCI
> >> specification, so it works with standard XHCI Linux driver.
> >>
> >> The host side of USBSS DRD controller is compliant with XHCI.
> >> The architecture for device side is almost the same as for host side,
> >> and most of the XHCI specification can be used to understand how
> >> this controller operates.
> >>
> >> This controller and driver support Full Speed, Hight Speed, Supper Speed
> >> and Supper Speed Plus USB protocol.
> >>
> >> The prefix cdnsp used in driver has chosen by analogy to cdn3 driver.
> >> The last letter of this acronym means PLUS. The formal name of controller
> >> is USBSSP but it's to generic so I've decided to use CDNSP.
> >>
> >> The patch 1: adds DT binding.
> >> The patch 2: adds PCI to platform wrapper used on Cadnece testing
> >> platform. It is FPGA based on platform.
> >> The patches 3-5: add the main part of driver and has been intentionally
> >> split into 3 part. In my opinion such division should not
> >> affect understanding and reviewing the driver, and cause that
> >> main patch (4/5) is little smaller. Patch 3 introduces main
> >> header file for driver, 4 is the main part that implements all
> >> functionality of driver and 5 introduces tracepoints.
> >
> >I'm more interested in how is this different from CDNS3. Aren't they SW compatible?
>
> In general, the controller can be split into 2 part- DRD part and the rest UDC.
>
> The second part UDC which consist gadget.c, ring.c and mem.c file is completely different.
>
> The DRD part contains drd.c and core.c.
> cdnsp drd.c is similar to cdns3 drd.c but it's little different. CDNSP has similar, but has different register space.
> Some register was moved, some was removed and some was added.
>
> core.c is very similar and eventually could be common for both drivers. I thought about this but
> I wanted to avoid interfering with cdns3 driver at this point CDNSP is still under testing and
> CDNS3 is used by some products on the market.

Pawel, I suggest adding CDNSP at driver/staging first since it is still
under testing. When you are thinking the driver (as well as hardware) are
mature, you could try to add gadget part (eg, gadget-v2) and make
necessary changes for core.c.

--

Thanks,
Peter Chen