[USB BOOT] Help needed

[Sascha Hauer]

Hi Vincente,

On Sat, Feb 11, 2017 at 02:50:12PM +0100, Vicente Bergas wrote:
> Hello
> 
> Background on the issue
> #######################
> 
> Some time ago functionality was added to enable OMAP4 to boot over USB:
> https://git.pengutronix.de/cgit/barebox/commit/?id=6b4dc4d4f128bd22df4d022ad37285ce4858e1e8
> That implementation uses the usb library stored in the OMAP4 ROM.
> The use of the OMAP4 ROM is problematic as it requires interrupts
> and also does not allow the MMU to be enabled.
> In fact there is an open issue with it:
> http://lists.infradead.org/pipermail/barebox/2016-August/027880.html
> 
> More recently a similar functionality was added to OMAP3:
> https://git.pengutronix.de/cgit/barebox/commit/?id=1d7c8ec1431aec1c75c79dc17ecad0ab80435311
> That implementation is using it's own way to access
> the usb device and has no dependencies on the ROM.
> 
> Proposed changes
> ################
> 
> Given this scenario I modified the OMAP4 code to access the
> usb device directly, bypassing the ROM library, the same way
> the OMAP3 code does.
> Both OMAP3 and OMAP4 use the same usb device (musb, mentor-usb),
> the only change is the base address.
> So this modification tries to make it generic for both OMAPs,
> although it has not been tested on OMAP3.
> The patch with this modification follows.
> 
> What is wrong with it
> #####################
> 
> Unfortunately, this modification is not working.
> The observed behaviour is:
> 1.- The console over usb works fine, as long as
> there is constant activity. If there are no transfers
> for approximately 4 seconds then the usb link is lost.

Do there have to be activity from the host to the device or is it enough
to do a "while true; do echo "huhu"; sleep 3; done" on the barebox
console?

I don't exactly know how this internally works, but with USB all
traffic is initiated by the host. If the device never answers a packet
since it has nothing to say at the moment it might happen that the host
thinks the device is dead. It's just an idea that you have to send some
dummy data every few seconds.

> 2.- The file system over usb works fine. Checked MD5 sums
> of kernel image and initial ram disk, all OK.
> 3.- Barebox reaches the start_linux function and executes
> the kernel function pointer, so, control is transferred
> to linux-land. But linux does not boot and
> nothing is printed on the serial console.

Have you tried earlyprintk in the Kernel? Do you also use the same
serial console in barebox, or do you only use console over USB?
Sometimes it happens that Linux does not have all initialization code so
that a device does not work in Linux when it hasn't been used in barebox
before.

Sascha


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