Re: [PATCH v10 6/7] usb: pci-quirks: add Intel USB drcfg mux device

Greg Kroah-Hartman
2016-06-08T15:45:30Z

On Wed, Jun 08, 2016 at 03:56:04PM +0800, Lu Baolu wrote:
> Hi Greg,
>
> On 06/08/2016 12:45 PM, Greg Kroah-Hartman wrote:
> > On Thu, Jun 02, 2016 at 09:37:28AM +0800, Lu Baolu wrote:
> >> In some Intel platforms, a single usb port is shared between USB host
> >> and device controllers. The shared port is under control of a switch
> >> which is defined in the Intel vendor defined extended capability for
> >> xHCI.
> >>
> >> This patch adds the support to detect and create the platform device
> >> for the port mux switch.
> > Why do you need a platform device for this? You do nothing with this
> > device, why create it at all?
>
> In this patch series, I have a generic framework for port mux devices
> and two port mux drivers sitting on top the generic code.
>
> In this patch, I create a platform device for the real mux device in
> Intel Cherry Trail or Broxton SOCs. In it's driver, I registered a mux
> into the generic framework and handle the power management
> things in driver's pm entries (otherwise, the system can't be waken
> up from system suspend).
>
> > And why is it a platform device, isn't is really a PCI device? Why
> > would you ever find a "platform" device below a PCI device? Don't abuse
> > platform devices for things that aren't. It makes me want to delete
> > that whole interface more and more...
>
> Port mux devices are physical devices in Intel Cherry Trail and Broxton
> SOCs. It doesn't sit on any PCIe bus. But it maps its registers in xHCI
> space. OS kernel can enumerate it by looking up the xhci extended
> capability list with a vendor specific capability ID.

A physical device that maps registers into PCI space seems like a PCI
device of some type to me :)

Again, I hate platform devices for obvious reasons like this...

greg k-h