linux-kernel - Re: [PATCH v8 3/9] usb: dwc3: core: Access XHCI address space temporarily to read port info

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Date:   Wed, 17 May 2023 09:46:59 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Felipe Balbi <balbi@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "quic_pkondeti@...cinc.com" <quic_pkondeti@...cinc.com>,
        "quic_ppratap@...cinc.com" <quic_ppratap@...cinc.com>,
        "quic_wcheng@...cinc.com" <quic_wcheng@...cinc.com>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>,
        "quic_harshq@...cinc.com" <quic_harshq@...cinc.com>,
        "ahalaney@...hat.com" <ahalaney@...hat.com>
Subject: Re: [PATCH v8 3/9] usb: dwc3: core: Access XHCI address space
 temporarily to read port info

On Wed, May 17, 2023 at 03:21:24AM +0000, Thinh Nguyen wrote:
> On Wed, May 17, 2023, Krishna Kurapati PSSNV wrote:
> > On 5/16/2023 8:32 PM, Krishna Kurapati PSSNV wrote:
> > > On 5/16/2023 5:41 PM, Johan Hovold wrote:

> > > > You should not make another copy of xhci_find_next_ext_cap(), but rather
> > > > use it directly.
> > > > 
> > > > We already have drivers outside of usb/host using this function so it
> > > > should be fine to do the same for now:
> > > > 
> > > >     #include "../host/xhci-ext-caps.h"

> > >    This was the approach which we followed when we first introduced the
> > > patch [1]. But Thinh suggested to duplicate code so that we can avoid
> > > any dependency on xhci (which seems to be right). So since its just one
> > > function, I duplicated it here.

> >   Would like to know your opinion here on how to proceed further.

> Please keep them separated. The xhci-ext-caps.h is for xhci driver only.
> It's not meant to be exposed to other drivers. Same with other *.h files
> under drivers/usb/host.

As I mentioned earlier, it is already used by the xdbc earlyprintk
driver which lives outside of drivers/usb/host, even if such a debug
driver could be considered a special case.

If it turns out that there's no way to avoid mapping those registers
from the qcom glue driver, then I think at least the register defines
need to be provided in a global header rather than being copied
verbatim.

But hopefully that can be avoided too as the xhci driver already parses
these registers and stores the port information, even if accessing that
data may require a bit more work currently.

Johan