linux-kernel - RE: [PATCH 3/8][v3]usb:fsl:otg: Add support to add/remove usb host driver

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Message-ID: <Pine.LNX.4.44L0.1508241030430.1628-100000@iolanthe.rowland.org>
Date:	Mon, 24 Aug 2015 10:35:48 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ramneek Mehresh <ramneek.mehresh@...escale.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Li Leo <LeoLi@...escale.com>
Subject: RE: [PATCH 3/8][v3]usb:fsl:otg: Add support to add/remove usb host
 driver

On Mon, 24 Aug 2015, Ramneek Mehresh wrote:

> > On Thu, 20 Aug 2015, Ramneek Mehresh wrote:
> > 
> > > > > --- a/drivers/usb/host/ehci-fsl.h
> > > > > +++ b/drivers/usb/host/ehci-fsl.h
> > > > > @@ -63,4 +63,22 @@
> > > > >  #define UTMI_PHY_EN             (1<<9)
> > > > >  #define ULPI_PHY_CLK_SEL        (1<<10)
> > > > >  #define PHY_CLK_VALID		(1<<17)
> > > > > +
> > > > > +struct ehci_fsl {
> > > > > +#ifdef CONFIG_PM
> > > > > +	/* Saved USB PHY settings, need to restore after deep sleep. */
> > > > > +	u32 usb_ctrl;
> > > > > +#endif
> > > >
> > > > Do you need this #ifdef?
> > > >
> > > Yes, this is required for deep-sleep support...we need to save/restore
> > controller
> > > registers during deep-sleep when usb controller power is shut-off. Don't
> > need this
> > > during normal usb operation...saving/restoring usb controller registers in
> > non deep-sleep
> > > scenario will add unnecessary delays
> > 
> > What I meant was, can you keep the "u32 usb_ctrl;" line but get rid of
> > the "#ifdef CONFIG_PM" and "#endif" lines?
> > 
> > Alan Stern
> I do understand that.

It doesn't sound like you do.

>  However, USB suspend/resume functionality work in context of
> PM. Only in this context, we need to save/restore usb controller register
> for deep-sleep functionality. If you see usage of this in ehci-fsl.c file, it's used in 
> ehci_fsl_drv_suspend() under CONFIG_PM to save USB CNTL register.

Yes, I know.

> If I remove CONFIG_PM from struct ehci_fsl{}, I'll need to change the entire driver
> also to make suspend and resume functionalities compile by default.

Why?  Suppose you remove the "#ifdef CONFIG_PM" and "#endif" lines but 
leave everything else the same.  Won't the driver still work?

If CONFIG_PM is enabled then everything will be exactly the same as it 
is now.  If CONFIG_PM isn't enabled then you will have an extra 
usb_ctrl field in the ehci_fsl structure.  It will never get used for 
anything but the driver should still work.  Right?

Alan Stern

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