linux-kernel - Re: [PATCH v16 6/7] usb: host: xhci-plat: Create platform device for onboard hubs in probe()

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Date:   Wed, 20 Oct 2021 16:05:37 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <balbi@...nel.org>
Cc:     devicetree@...r.kernel.org, Peter Chen <peter.chen@...nel.org>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Bastien Nocera <hadess@...ess.net>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Michal Simek <michal.simek@...inx.com>,
        Douglas Anderson <dianders@...omium.org>,
        Roger Quadros <rogerq@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Osipenko <digetx@...il.com>,
        Fabio Estevam <festevam@...il.com>
Subject: Re: [PATCH v16 6/7] usb: host: xhci-plat: Create platform device for
 onboard hubs in probe()

Hi

On 13.8.2021 22.52, Matthias Kaehlcke wrote:
> Call onboard_hub_create/destroy_pdevs() from  _probe()/_remove()
> to create/destroy platform devices for onboard USB hubs that may
> be connected to the root hub of the controller. These functions
> are a NOP unless CONFIG_USB_ONBOARD_HUB=y/m.
> 
> Also add a field to struct xhci_hcd to keep track of the onboard hub
> platform devices that are owned by the xHCI.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---

Haven't really looked at this series until now.

Is there any reason why the xhci platform driver was selected as 
the best place to create/remove these onboard hub devices?

This ties the onboard hubs to xhci, and won't work in case we have onboard
hubs connected to a ehci controllers.

If separate devices for controlling onboard hub power is the right solution then
how about creating the onboard hub device in usb_add_hcd() (hcd.c), and
store it in struct usb_hcd.

A bit like how the roothub device is created, or PHYs are tuned.

Thanks
Mathias