[PATCH V3 2/5] ARM: dts: bcm283x: Add dtsi for USB host mode

[Stefan Wahren]

Hi Eric,

> Eric Anholt <eric at anholt.net> hat am 22. August 2016 um 19:57 geschrieben:
> 
> 
> Stefan Wahren <stefan.wahren at i2se.com> writes:
> 
> > In case dr_mode isn't passed via DT, the dwc2 defaults to OTG mode.
> > But all Raspberry Pi boards here are designed only for host mode.
> > So fix this issue by providing a dtsi file which set the dr_mode
> > to host.
> 
> Can you explain what change this should cause for these boards?  Is it
> just going to drop this message from dmesg:
> 
> dwc2 3f980000.usb: Configuration mismatch. dr_mode forced to host

IMO it isn't a message which could be ignored. The dwc2 tries to detected the
USB role from compile configuration and hardware capabilities, but according to
the decision table [1] we should provide the correct dr_mode which is import for
FIFO configuration and so on.

Another problem that i see is that the USB behavior is influenced by compile
settings in a unexpected way. With arm/configs/bcm2835_defconfig the driver is
forced to host, but in a multiplatform config like arm64/configs/defconfig not.
I would expect a more stable dr_mode.

At the end the dwc2 can't reliable detect the dr_mode because it depends on the
board design.

Any concerns?

Stefan

[1] -
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=5268ed9d2e3b52f703f3661eef14cecbb2b572d4

> 
> or something else?
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