Re: [PATCH 1/1] usb: chipidea: host: add own hc_driver for each hcd

[Peter Chen <peter.chen@freescale.com>]

On Sun, Jul 19, 2015 at 10:22:47PM -0400, Alan Stern wrote:
> On Mon, 20 Jul 2015, Peter Chen wrote:
> 
> > On Fri, Jul 17, 2015 at 09:52:26AM -0400, Alan Stern wrote:
> > > On Fri, 17 Jul 2015, Peter Chen wrote:
> > > 
> > > > There are several benefits for doing like this:
> > > > 
> > > > - hc_driver can be customized for each hcd
> > > > - Other hcd hc_driver's initialization will not affect current one.
> > > > We run out NULL pointer dereference problem when one hcd is started
> > > > by module_init, and the other is started by otg thread at SMP platform.
> > > > The reason for this problem is ehci_init_driver will do memory copy
> > > > for current uniform hc_driver, and this memory copy will do memset (as 0)
> > > > first, so when the first hcd is running usb_add_hcd, and the second
> > > > hcd may clear the uniform hc_driver's space (at ehci_init_driver),
> > > > then the first hcd will meet NULL pointer at the same time.
> > > 
> > > It seems to me the real problem is that ehci_init_driver gets called at
> > > the wrong time.  It's not supposed to be called whenever a new host
> > > controller is initialized; rather, it should be called just once when
> > > the driver is initialized.  This means the call should be in a
> > > module_init routine in host.c, not in ci_hdrc_host_init.
> > > 
> > 
> > But we have no platform driver dedicated for host controller, is it a
> > must? The core driver requests io_address, interrupt, dma_mask, etc for
> > both device and host driver, and device and host part (we does not take
> > it as a driver) should not request resources again.
> 
> It doesn't matter.  There's no harm in calling ehci_init_driver, even
> if the hardware doesn't contain a host controller.  The point is that
> this call should be made only once, when the main ci_hdrc driver starts
> up.  It should not be made every time a platform driver registers a
> host controller.
> 
> > Would you accept it as another use case for ehci driver?
> 
> I don't think a new use case is needed.  All you have to do is add
> something like this to host.c:
> 
> static void ci_hdrc_host_driver_init(void)
> {
> 	ehci_init_driver(&ci_ehci_hc_driver, &ehci_ci_overrides);
> }
> module_init(ci_hdrc_host_driver_init);
> 
> Can you think of any reason this won't work?
> 

No, it will not work. The core driver's probe will run which will
call host_start to call ehci APIs before ci_hdrc_host_driver_init
is called.

-- 

Best Regards,
Peter Chen