From: Ramneek Mehresh <ramneek.mehresh@freescale.com>
To: Alan Stern <stern@rowland.harvard.edu>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "balbi@ti.com" <balbi@ti.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Subject: RE: [PATCH 2/9][v2]usb:fsl:otg: Add support to add/remove usb host
 driver
Thread-Topic: [PATCH 2/9][v2]usb:fsl:otg: Add support to add/remove usb host
 driver
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Date: Mon, 20 Apr 2015 16:35:24 +0000
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> -----Original Message-----
> From: Alan Stern [mailto:stern@rowland.harvard.edu]
> Sent: Tuesday, April 07, 2015 9:23 PM
> To: Mehresh Ramneek-B31383
> Cc: linux-kernel@vger.kernel.org; linux-usb@vger.kernel.org; balbi@ti.com;
> gregkh@linuxfoundation.org
> Subject: Re: [PATCH 2/9][v2]usb:fsl:otg: Add support to add/remove usb
> host driver
> 
> On Tue, 7 Apr 2015, Ramneek Mehresh wrote:
> 
> > Add workqueue to add/remove host driver (outside interrupt context)
> > upon each id change
> 
> This patch needs to be fixed.  See below.
> 
Thanks Alan.  I'll correct the patch.

> > Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
> > ---
> >  drivers/usb/host/ehci-fsl.c | 107
> ++++++++++++++++++++++++++++++++++++--------
> >  drivers/usb/host/ehci.h     |   1 -
> >  2 files changed, 88 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/usb/host/ehci-fsl.c b/drivers/usb/host/ehci-fsl.c
> > index ab4eee3..9c91fbe 100644
> > --- a/drivers/usb/host/ehci-fsl.c
> > +++ b/drivers/usb/host/ehci-fsl.c
> > @@ -33,6 +33,58 @@
> >
> >  #include "ehci-fsl.h"
> >
> > +struct ehci_fsl {
> > +	struct ehci_hcd ehci;
> > +
> > +#ifdef CONFIG_PM
> > +	/* Saved USB PHY settings, need to restore after deep sleep. */
> > +	u32 usb_ctrl;
> > +#if defined(CONFIG_FSL_USB2_OTG) ||
> defined(CONFIG_FSL_USB2_OTG_MODULE)
> > +	struct work_struct change_hcd_work;
> > +#endif
> > +#endif
> > +
> > +	/* store current hcd state for otg;
> > +	 * have_hcd is true when host drv al already part of otg framework,
> > +	 * otherwise false;
> > +	 * hcd_add is true when otg framework wants to add host
> > +	 * drv as part of otg;flase when it wants to remove it
> > +	 */
> > +	unsigned have_hcd:1;
> > +	unsigned hcd_add:1;
> > +};
> 
> This is the wrong way to connect platform-private data with the ehci_hcd
> structure.  The right way is to use an ehci_driver_overrides structure, like in
> ehci-omap.c and quite a few other EHCI platform drivers.
> 
Will correct
> > +#if defined(CONFIG_FSL_USB2_OTG) ||
> > +defined(CONFIG_FSL_USB2_OTG_MODULE)
> > +static struct ehci_fsl *hcd_to_ehci_fsl(struct usb_hcd *hcd) {
> > +	struct ehci_hcd *ehci = hcd_to_ehci(hcd);
> > +
> > +	return container_of(ehci, struct ehci_fsl, ehci); }
> 
> This is bound to fail no matter what, because the ehci_hcd structure is
> already embedded in the usb_hcd structure.  It can't be embedded in an
> ehci_fsl structure too.
> 
> (Of course, this won't matter when you switch to the approved way of
> connecting private data.)
> 
Will correct
> > +static void do_change_hcd(struct work_struct *work) {
> > +	struct ehci_fsl *ehci_fsl = container_of(work, struct ehci_fsl,
> > +					change_hcd_work);
> > +	struct ehci_hcd *ehci = &ehci_fsl->ehci;
> > +	struct usb_hcd *hcd = ehci_to_hcd(ehci);
> > +
> > +	void __iomem *non_ehci = hcd->regs;
> > +	int retval;
> > +
> > +	if (ehci_fsl->hcd_add && !ehci_fsl->have_hcd) {
> > +		writel(USBMODE_CM_HOST, non_ehci +
> FSL_SOC_USB_USBMODE);
> > +		/* host, gadget and otg share same int line */
> > +		retval = usb_add_hcd(hcd, hcd->irq, IRQF_SHARED);
> > +		if (retval == 0)
> > +			ehci_fsl->have_hcd = 1;
> > +	} else if (!ehci_fsl->hcd_add && ehci_fsl->have_hcd) {
> > +		usb_remove_hcd(hcd);
> > +		ehci_fsl->have_hcd = 0;
> > +	}
> > +}
> 
> Does this really work right?  What about things like
> device_wakeup_enable()?  Don't you need to disable the controller when
> leaving host mode and enable it when entering host mode?
> 
Yes, this does work, it's tested. Yes, controller needs to be disabled when switching the mode from
Host to gadget and vice-versa. Only one driver can have control of the hardware at a time. that's why call 
to usb_remove_hcd() is made. Gadget driver configures the controller in gadget mode, and takes control of
the hardware
> Alan Stern

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