linux-kernel - Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

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Message-ID: <20140926003934.GD12770@saruman>
Date:	Thu, 25 Sep 2014 19:39:34 -0500
From:	Felipe Balbi <balbi@...com>
To:	Felipe Balbi <balbi@...com>
CC:	Peter Chen <peter.chen@...escale.com>,
	Arnd Bergmann <arnd@...db.de>,
	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<sebastian.hesselbarth@...il.com>, <p.zabel@...gutronix.de>,
	<thomas.petazzoni@...e-electrons.com>, <zmxu@...vell.com>,
	<devicetree@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<alexandre.belloni@...e-electrons.com>, <jszhang@...vell.com>
Subject: Re: [PATCH v6 07/12] usb: chipidea: add a usb2 driver for ci13xxx

Hi again,

On Thu, Sep 25, 2014 at 07:37:50PM -0500, Felipe Balbi wrote:
> On Fri, Sep 26, 2014 at 07:39:34AM +0800, Peter Chen wrote:
> > On Thu, Sep 25, 2014 at 09:15:53AM -0500, Felipe Balbi wrote:
> > > On Wed, Sep 24, 2014 at 02:23:38PM +0200, Arnd Bergmann wrote:
> > > > On Wednesday 24 September 2014 19:29:05 Peter Chen wrote:
> > > > > 
> > > > > So, it is IP CORE LIB (you suggest) vs IP CORE Platform Driver
> > > > > (dwc3, musb, chipidea) you are talking about, right? Except for
> > > > > creating another platform driver as well as related DT node (optional),
> > > > > are there any advantages compared to current IP core driver structure?
> > > > 
> > > > Having a library module usually requires less code, and is more
> > > > consistent with other drivers, which helps new developers understand
> > > > what the driver is doing.
> > > 
> > > I beg to differ. You end-up having to pass function pointers through
> > > platform_data to handle differences which could be handled by the core
> > > IP.
> > > 
> > > > The most important aspect though is the DT binding: once the structure
> > > > with separate kernel drivers leaks out into the DT format, you can't
> > > > easily change the driver any more, e.g. to make a property that was
> > > > introduced for one glue driver more general so it can get handled by
> > > > the common part. Having a single node lets us convert to the library
> > > > model later, so that would be a strong reason to keep the DT binding
> > > > simple, without child nodes.
> > > > 
> > > > Following that logic, it turns into another reason for using the library
> > > > model to start with, because otherwise the child device does not have
> > > > any DT properties itself and has to rely on the parent device properties,
> > > > which somewhat complicates the driver structure.
> > > 
> > > this is bullcrap. Take a look at
> > > Documentation/devicetree/bindings/usb/dwc3.txt:
> > > 
> > > synopsys DWC3 CORE
> > > 
> > > DWC3- USB3 CONTROLLER
> > > 
> > > Required properties:
> > >  - compatible: must be "snps,dwc3"
> > >  - reg : Address and length of the register set for the device
> > >  - interrupts: Interrupts used by the dwc3 controller.
> > > 
> > > Optional properties:
> > >  - usb-phy : array of phandle for the PHY device.  The first element
> > >    in the array is expected to be a handle to the USB2/HS PHY and
> > >    the second element is expected to be a handle to the USB3/SS PHY
> > >  - phys: from the *Generic PHY* bindings
> > >  - phy-names: from the *Generic PHY* bindings
> > >  - tx-fifo-resize: determines if the FIFO *has* to be reallocated.
> > > 
> > > This is usually a subnode to DWC3 glue to which it is connected.
> > > 
> > > dwc3@...30000 {
> > > 	compatible = "snps,dwc3";
> > > 	reg = <0x4a030000 0xcfff>;
> > > 	interrupts = <0 92 4>
> > > 	usb-phy = <&usb2_phy>, <&usb3,phy>;
> > > 	tx-fifo-resize;
> > > };
> > > 
> > > This contains all the attributes it needs to work. In fact, this could
> > > be used without any glue.
> > > 
> > 
> > If you want to add "vbus-supply" core node to support ID switch, what's
> > the plan for that?
> 
> send a patch ? Just make sure it's optional because not everybody needs
> a vbus-supply. Also, DRD will still take a few merge windows to become a
> reality. I don't want to merge something before considering it carefuly,
> otherwise we will having which is broken and doesn't work for everybody
> ;-)
> 
> > Is it possible that the glue layer needs to access core register
> > (eg, portsc.phcd during suspend)? The wrapper IP may wait some signals
> > at core IP to change.
> 
> why would a glue layer need to access registers from the core ? That
> sounds very odd. I haven't seen that and will, definitely, NACK such a
> patch :-)
> 
> can you further describe why you think a glue layer might need to access
> core IP's registers ?

I just realised we're talking about chipidea here... in any case, it's
still valid to ask why would glue need to fiddle with core IP's
registers.

-- 
balbi

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