linux-kernel - Re: [PATCH 3/3] usb: musb: fix setting JZ4740 gadget periphal mode on reset

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Date:	Tue, 17 Dec 2013 02:31:00 +0100
From:	Apelete Seketeli <apelete@...eteli.net>
To:	Felipe Balbi <balbi@...com>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH 3/3] usb: musb: fix setting JZ4740 gadget periphal mode
 on reset

On 16-Dec-13, Felipe Balbi wrote:
> On Sat, Dec 14, 2013 at 04:48:38AM +0100, Apelete Seketeli wrote:
> > JZ4740 USB Device Controller is not OTG compatible and does not have DEVCTL
> > register in silicon.
> > 
> > During ethernet-over-usb transactions, on reset, musb driver tries to
> > read from DEVCTL and consequently sets device as host (A-Device)
> > instead of peripheral (B-Device), which makes it a composite device to
> > the USB gadget driver.
> > This induces a kernel panic during power down where the USB gadget
> > driver does a null pointer dereference when trying to access the
> > composite device configuration.
> > 
> > On reset, do not rely on DEVCTL value for setting gadget peripheral
> > mode: hardcode it instead to B-Device.
> > 
> > Signed-off-by: Apelete Seketeli <apelete@...eteli.net>
> > ---
> >  drivers/usb/musb/musb_gadget.c |    9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
> > index 32fb057..b4bea7a 100644
> > --- a/drivers/usb/musb/musb_gadget.c
> > +++ b/drivers/usb/musb/musb_gadget.c
> > @@ -2119,6 +2119,14 @@ __acquires(musb->lock)
> >  	/* Normal reset, as B-Device;
> >  	 * or else after HNP, as A-Device
> >  	 */
> > +#if defined(CONFIG_USB_MUSB_JZ4740) || defined(CONFIG_USB_MUSB_JZ4740_MODULE)
> 
> NAK, no ifdefs in this driver. Pass a quirk flag through platform_data
> or something similar.

I get that, makes sense to me, but problem is the driver has to read a
valid value from DEVCTL hardware register when musb_g_reset() is
called, and I do not see how this can be achieved through
platform_data.

Is it ok to use ifdefs in musb_regs.h to add specific hardware
register indexes for JZ4740 instead ?
I am actually thinking about fooling the musb driver into reading a
valid value from another register instead of DEVCTL.

Cheers.
-- 
        Apelete
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