RE: [PATCH v12 1/3] misc: Add versal-usb2-ctrl-regs module

[Sai Pavan Boddu <saipava@xilinx.com>]

Hi Peter,

> -----Original Message-----
> From: Peter Maydell <peter.maydell@linaro.org>
> Sent: Wednesday, October 28, 2020 6:44 PM
> To: Sai Pavan Boddu <saipava@xilinx.com>
> Cc: Markus Armbruster <armbru@redhat.com>; Marc-André Lureau
> <marcandre.lureau@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>;
> Gerd Hoffmann <kraxel@redhat.com>; Edgar Iglesias <edgari@xilinx.com>;
> Francisco Eduardo Iglesias <figlesia@xilinx.com>; QEMU Developers <qemu-
> devel@nongnu.org>; Alistair Francis <alistair.francis@wdc.com>; Eduardo
> Habkost <ehabkost@redhat.com>; Ying Fang <fangying1@huawei.com>;
> Philippe Mathieu-Daudé <philmd@redhat.com>; Vikram Garhwal
> <fnuv@xilinx.com>; Paul Zimmerman <pauldzim@gmail.com>
> Subject: Re: [PATCH v12 1/3] misc: Add versal-usb2-ctrl-regs module
> 
> On Wed, 28 Oct 2020 at 12:58, Sai Pavan Boddu <saipava@xilinx.com> wrote:
> >
> > Hi Peter,
> >
> > > -----Original Message-----
> > > From: Sai Pavan Boddu
> > > Sent: Monday, October 26, 2020 10:59 PM
> > > To: Peter Maydell <peter.maydell@linaro.org>
> > > Cc: Markus Armbruster <armbru@redhat.com>; Marc-André Lureau
> > > <marcandre.lureau@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>;
> > > Gerd Hoffmann <kraxel@redhat.com>; Edgar Iglesias
> > > <edgari@xilinx.com>; Francisco Eduardo Iglesias
> > > <figlesia@xilinx.com>; QEMU Developers <qemu- devel@nongnu.org>;
> > > Alistair Francis <alistair.francis@wdc.com>; Eduardo Habkost
> > > <ehabkost@redhat.com>; Ying Fang <fangying1@huawei.com>; Philippe
> > > Mathieu-Daudé <philmd@redhat.com>; Vikram Garhwal
> <fnuv@xilinx.com>;
> > > Paul Zimmerman <pauldzim@gmail.com>
> > > Subject: RE: [PATCH v12 1/3] misc: Add versal-usb2-ctrl-regs module
> > >
> > > Hi Peter,
> > >
> > > > -----Original Message-----
> > > > From: Peter Maydell <peter.maydell@linaro.org>
> > > > Sent: Monday, October 26, 2020 9:33 PM
> > > > To: Sai Pavan Boddu <saipava@xilinx.com>
> > > > Cc: Markus Armbruster <armbru@redhat.com>; Marc-André Lureau
> > > > <marcandre.lureau@redhat.com>; Paolo Bonzini
> > > > <pbonzini@redhat.com>; Gerd Hoffmann <kraxel@redhat.com>; Edgar
> > > > Iglesias <edgari@xilinx.com>; Francisco Eduardo Iglesias
> > > > <figlesia@xilinx.com>; QEMU Developers
> > > > <qemu- devel@nongnu.org>; Alistair Francis
> > > > <alistair.francis@wdc.com>; Eduardo Habkost <ehabkost@redhat.com>;
> > > > Ying Fang <fangying1@huawei.com>; Philippe Mathieu-Daudé
> > > > <philmd@redhat.com>; Vikram Garhwal <fnuv@xilinx.com>; Paul
> > > > Zimmerman
> > > <pauldzim@gmail.com>;
> > > > Sai Pavan Boddu <saipava@xilinx.com>
> > > > Subject: Re: [PATCH v12 1/3] misc: Add versal-usb2-ctrl-regs
> > > > module
> > > >
> > > > On Thu, 22 Oct 2020 at 13:11, Sai Pavan Boddu
> > > > <sai.pavan.boddu@xilinx.com>
> > > > wrote:
> > > > >
> > > > > This module emulates control registers of versal usb2
> > > > > controller, this is added just to make guest happy. In general
> > > > > this module would control the phy-reset signal from usb
> > > > > controller, data coherency of the transactions, signals the host system
> errors received from controller.
> > > > >
> > > > > Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@xilinx.com>
> > > > > Signed-off-by: Vikram Garhwal <fnu.vikram@xilinx.com>
> > > > > ---
> > > > >  hw/misc/meson.build                          |   1 +
> > > > >  hw/misc/xlnx-versal-usb2-ctrl-regs.c         | 229
> > > > +++++++++++++++++++++++++++
> > > > >  include/hw/misc/xlnx-versal-usb2-ctrl-regs.h |  45 ++++++
> > > >
> > > > This seems a bit odd. If it's a USB device (or part of a USB
> > > > device) then it should be under hw/usb, shouldn't it?
> > > [Sai Pavan Boddu] This is a top level wrapper over hcd-dwc3 device,
> > > which is specific to versal soc. It's mostly dummy which controls
> > > the phy-reset and does frame length adjustments. It was added just
> > > to make guest happy, that is the reason it has been added to misc devices.
> > > >
> > > > > +static void ir_status_postw(RegisterInfo *reg, uint64_t val64) {
> > > > > +    VersalUsb2CtrlRegs *s = XILINX_VERSAL_USB2_CTRL_REGS(reg-
> > > >opaque);
> > > > > +    /*
> > > > > +     * TODO: This should also clear USBSTS.HSE field in USB XHCI
> register.
> > > > > +     * May be combine both the modules.
> > > > > +     */
> > > >
> > > > What does the hardware for this look like? You've modelled it as
> > > > two completely separate devices (this one and the
> > > > TYPE_USB_DWC3) but would it be closer to the hardware structure to
> > > > have a top-level device which has-a DWC3 ?
> > > [Sai Pavan Boddu] Yes, we can look at it such way. But as its
> > > specific to versal SOC, we have crafted it out and stitched them in SOC file.
> > >
> > > Regards,
> > > Sai Pavan
> > [Sai Pavan Boddu] I would be sending V13 without doing any changes with
> this patch and addressing other comments, Please review over V13.
> 
> You have my review comments above. I think the way you've structured this
> isn't really the best way to do it.
[Sai Pavan Boddu] Ok, I would move this into USB folder as its related. 
But this device is not like a top level module of DWC3 model, is used for handling phy-reset signal & power management of usb port.
It's not a good idea to embedded this device into DWC3 module.

Anyway, I would attempt to create a subsystem by making dwc3 and usb2-ctrl-regs child of one device.

Regards,
Sai Pavan

> 
> thanks
> -- PMM