[U-Boot] Doubt in USB driver for Vybrid vf610

[maitysanchayan at gmail.com]

On 15-10-24 19:50:13, Marek Vasut wrote:
> On Saturday, October 24, 2015 at 06:23:44 PM, maitysanchayan at gmail.com wrote:
> > On 15-10-24 18:16:20, Marek Vasut wrote:
> > > On Saturday, October 24, 2015 at 06:08:57 PM, maitysanchayan at gmail.com 
> wrote:
> > > > On 15-10-24 18:08:53, Marek Vasut wrote:
> > > > > On Saturday, October 24, 2015 at 05:23:05 PM,
> > > > > maitysanchayan at gmail.com
> > > 
> > > wrote:
> > > > > > Hello,
> > > > > > 
> > > > > > On 15-10-24 12:09:43, Fabio Estevam wrote:
> > > > > > > Hi Marek,
> > > > > > > 
> > > > > > > On Fri, Oct 23, 2015 at 4:23 PM, Marek Vasut <marex at denx.de> wrote:
> > > > > > > >> Any inputs on the below?
> > > > > > > > 
> > > > > > > > I don't have a Vybrid device, CCing Fabio.
> > > > > > > 
> > > > > > > I don't have access to a Vybrid board either.
> > > > > > > 
> > > > > > > Sanchayan,
> > > > > > > 
> > > > > > > Does drivers/usb/host/ehci-mx6.c behave the same way?
> > > > > > 
> > > > > > No.
> > > > > > 
> > > > > > I included the particular piece of code below
> > > > > > 
> > > > > > 	if (init == USB_INIT_DEVICE && index == 1)
> > > > > > 	
> > > > > > 		return -ENODEV;
> > > > > > 	
> > > > > > 	if (init == USB_INIT_HOST && index == 0)
> > > > > > 	
> > > > > > 		return -ENODEV;
> > > > > > 
> > > > > > in the ehci-vf driver because our requirement was to have one port
> > > > > > as client and other as host. Since on USB start both ports get
> > > > > > configured as host as it iterates depending on USB EHCI controller
> > > > > > count, the above was meant to stop the port required as client to
> > > > > > be configured as host and vice versa while using client
> > > > > > functionality such as DFU.
> > > > > > 
> > > > > > I made the mistake of not thinking that this is not a generic use
> > > > > > case, someone might want it the other way around or such.
> > > > > > 
> > > > > > So coming to the main question, what would be the correct way to
> > > > > > fix this? I tested that even if the above four lines are removed
> > > > > > and USB start configures both ports as host, calling dfu later
> > > > > > will still result in correct functioning. So is this ok and the
> > > > > > four lines should be nuked or a more appropriate way would be to
> > > > > > add something like board_ehci_hcd_init_with_type(int index, enum
> > > > > > usb_init _type init) which would be a weak function and have the
> > > > > > board specific code call this to do the above which is currently
> > > > > > done in ehci-vf.
> > > > > > 
> > > > > > I wasn't sure about the right approach to take so I asked.
> > > > > 
> > > > > Brief glare over the driver tells me that those four lines are
> > > > > complete nonsense and should be removed.
> > > > 
> > > > Yes very much so. But is removing just ok or it would be better to
> > > > actually restrict as per a board's requirement what gets configured as
> > > > host and what gets configured as client by adding the weak function
> > > > hook I was talking about?
> > > 
> > > The mx6 ones does board_usb_phy_mode() to determine this restriction. But
> > > (!) it'd be even better if this information was obtained from DT. It'd
> > > be nice if someone started working on converting i.MX to DT.
> > 
> > Yes, that's how iMX6 does it. However note that Vybrid USB is not a true
> > OTG.
> > 
> > I quote the Vybrid TRM here,
> > 
> > "The USB is not a true OTG. It can be configured by software to function
> > either as a peripheral or as host. The ID pin, which is unique for OTG
> > operation, is not present in this implementation. There are no five pin
> > interface. The user will get four pin host/device interface."
> 
> Can't the user use a GPIO instead of dedicated OTG switch pin ?

Yes. In fact in Linux we use the extcon framework along with the GPIO to have
automatic switch over between client and host.

I will send a patch by Monday to remove the incorrect code. Will later send
a patch to incoporate the correct fix. Since all boards might not have a GPIO
to do this I had not considered this option but if this is acceptable it is
fine by me.

Thanks.

- Sanchayan.