[Gta04-owner] Power supply for internal USB PHY

NeilBrown neilb at suse.de
Thu Jan 17 01:51:41 CET 2013

Hi Nikolaus,
 I've been exploring the possibility of enabling "off-mode" for the OMAP3
 which hopefully will save a bit of power.  It mostly works, however the two
 USB ports (internal and external) don't survive the transition through off
 mode yet.

 As a result of raising this issue - of the internal USB particularly - on
 the linux-omap list, it seems that it might be necessary to power-cycle the
 internal USB transceiver (USB3221).  You can read the thread starting:


 The best explanation that I can come up with is that when the 'CORE'
 power-domain of the OMAP3 turns off and  comes back on it loses sync with
 the USB phy in a way that 'reset' is insufficient to fix and a power-cycle
 is needed.   Seems strange and I'm not completely certain that this is the
 case, but the evidence seems to point that way.

 So it appears that it would be useful to be able to independently
 power-cycle the USB phy in much the same way that you can now power-cycle
 the Modem.

 As I say, I'm not completely sure so this isn't yet a "must have" for the
 GTA04a5, but it could be useful if it isn't too hard.

 On a related topic, my reading of the documentation for the USB3221 suggests
 that the VDD3V3 pin is a power *output*, not a power *input*, whereas the
 schematics show it wired like an input for the GTA04a[34].  I wouldn't
 expect this to be a serious problem, but it seems wrong and could possibly
 cause an unexpected power leakage.


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