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From:   Peter Chen <peter.chen@nxp.com>
To:     Pawel Laszczak <pawell@cadence.com>
CC:     "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Felipe Balbi <balbi@kernel.org>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "dan.carpenter@oracle.com" <dan.carpenter@oracle.com>,
        "ben.dooks@codethink.co.uk" <ben.dooks@codethink.co.uk>,
        "colin.king@canonical.com" <colin.king@canonical.com>,
        "rogerq@ti.com" <rogerq@ti.com>,
        "weiyongjun1@huawei.com" <weiyongjun1@huawei.com>,
        Jayshri Dajiram Pawar <jpawar@cadence.com>,
        Rahul Kumar <kurahul@cadence.com>,
        Sanket Parmar <sparmar@cadence.com>
Subject: Re: [PATCH RFC 0/5] Introduced new Cadence USBSSP DRD Driver.
Thread-Topic: [PATCH RFC 0/5] Introduced new Cadence USBSSP DRD Driver.
Thread-Index: AQHWS3Ylp2LS5pecmkenOlfLMCntJajqdbIAgAAHxACABHoqgIAADdgAgIYl9gCAAOewAA==
Date:   Wed, 23 Sep 2020 02:56:34 +0000
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On 20-09-22 13:06:26, Pawel Laszczak wrote:
> Hi,
>=20
> >
> >On Mon, Jun 29, 2020 at 03:41:49AM +0000, Peter Chen wrote:
> >> 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 an=
d
> >> > >> Host Only (XHCI)configurations.
> >> > >>
> >> > >> The current driver has been validated with FPGA burned. We have s=
upport
> >> > >> 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 s=
ide,
> >> > >> and most of the XHCI specification can be used to understand how
> >> > >> this controller operates.
> >> > >>
> >> > >> This controller and driver support Full Speed, Hight Speed, Suppe=
r Speed
> >> > >> and Supper Speed Plus USB protocol.
> >> > >>
> >> > >> The prefix cdnsp used in driver has chosen by analogy to cdn3 dri=
ver.
> >> > >> The last letter of this acronym means PLUS. The formal name of co=
ntroller
> >> > >> 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 intenti=
onally
> >> > >>              split into 3 part. In my opinion such division shoul=
d not
> >> > >>              affect understanding and reviewing the driver, and c=
ause that
> >> > >>              main patch (4/5) is little smaller. Patch 3 introduc=
es main
> >> > >>              header file for driver, 4 is the main part that impl=
ements all
> >> > >>              functionality of driver and 5 introduces tracepoints=
.
> >> > >
> >> > >I'm more interested in how is this different from CDNS3. Aren't the=
y SW compatible?
> >> >
> >> > In general, the controller can be split into 2 part- DRD part and th=
e 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. CDN=
SP 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 drive=
rs.  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 stil=
l
> >> 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.
> >
> >I only take code for drivers/staging/ that for some reason is not
> >meeting the normal coding style/rules/whatever.  For stuff that is an
> >obvious duplicate of existing code like this, and needs to be
> >rearchitected.  It is much more work to try to convert code once it is
> >in the tree than to just do it out of the tree on your own and resubmit
> >it, as you don't have to follow the in-kernel rules of "one patch does
> >one thing" that you would if it was in staging.
> >
> >So don't think that staging is the right place for this, just spend a
> >few weeks to get it right and then resubmit it.
> >
>=20
> I had idea to reuse indirect the core.c and drd.c in cdnsp driver. Of cou=
rse, I've made
> the necessary changes to make possible reuse this code.
> My approach was to add this file in Makefile in cdnsp but this concept fa=
iled.=20
> It even worked until I started testing cdns3 and cdnsp as build in kernel=
 :)
>=20
> With this approach I have issue with " multiple definition of .. "
>=20
> How should it look like such reusable code ?
>=20
> After my experience with above concept I think that only way is to move c=
ommon code
> to separate module,  similar as it is in drivers/usb/common directory or =
libcomposite.ko module.
>=20

Could you use compatible string or IP revision number to dynamic judge
which part of code you should use? That is to say there is only one
Cadence 3 USB driver folder -- cdns3, you only add one gadget file for
cdnsp revision?

--=20

Thanks,
Peter Chen=