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

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Message-ID: <5761F27D.6090602@linux.intel.com>
Date:	Thu, 16 Jun 2016 08:27:41 +0800
From:	Lu Baolu <baolu.lu@...ux.intel.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	felipe.balbi@...ux.intel.com,
	Mathias Nyman <mathias.nyman@...el.com>,
	Lee Jones <lee.jones@...aro.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 6/7] usb: pci-quirks: add Intel USB drcfg mux device

Hi Greg,

On 06/09/2016 10:39 AM, Lu Baolu wrote:
> Hi Greg,
>
> On 06/08/2016 11:45 PM, Greg Kroah-Hartman wrote:
>> 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...
>>
> It's not PCI configure space, but xhci's io memory. XHCI spec reserves
> a range in its extended capability list for vendor specific things. Intel's
> platform leverages this for the port mux device register mapping.
> It looks odd though. :)

A gentle ping. :)

This port mux is not a PCI device. It only leverages the vendor
specific capability defined in xhci specification for enumeration.

Best regards,
Lu Baolu