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

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Message-ID: <20200629034213.GB30684@b29397-desktop>
Date:   Mon, 29 Jun 2020 03:41:49 +0000
From:   Peter Chen <peter.chen@....com>
To:     Pawel Laszczak <pawell@...ence.com>
CC:     Felipe Balbi <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
        "ben.dooks@...ethink.co.uk" <ben.dooks@...ethink.co.uk>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        "rogerq@...com" <rogerq@...com>,
        "weiyongjun1@...wei.com" <weiyongjun1@...wei.com>,
        Jayshri Dajiram Pawar <jpawar@...ence.com>,
        Rahul Kumar <kurahul@...ence.com>,
        Sanket Parmar <sparmar@...ence.com>
Subject: Re: [PATCH RFC 0/5] Introduced new Cadence USBSSP DRD Driver.

On 20-06-26 07:19:56, Pawel Laszczak wrote:
> Hi Felipe,
> 
> >
> >Hi,
> >
> >Pawel Laszczak <pawell@...ence.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