> -----Original Message----- > From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] > Sent: Thursday, January 17, 2013 9:34 PM > To: Felipe Balbi > Cc: Venu Byravarasu; gregkh@xxxxxxxxxxxxxxxxxxx; linux- > usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > swarren@xxxxxxxxxxxxx; linux-tegra@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v2 4/4] usb: Add APIs to access host registers from Tegra > PHY > > On Thu, 17 Jan 2013, Felipe Balbi wrote: > > > On Thu, Jan 17, 2013 at 10:21:53AM -0500, Alan Stern wrote: > > > On Thu, 17 Jan 2013, Felipe Balbi wrote: > > > > > > > > Bits 31 & 30 from PORTSC register were allocated by our SOC > designers > > > > > to inform the host controller about the PHY type to be used. > > > > > > > > Wow, that's something you should never do. PORTSC register belongs > to > > > > the EHCI controller and those bits are reserved for future use and they > > > > *MUST* return zero. I wouldn't be surprised if current EHCI driver > > > > assumes those bits will be zero and/or makes sure they're set to zero > > > > when writing to PORTSC register. > > > > > > In fact, those bits _have_ been assigned an official purpose in the > > > EHCI-1.1 addendum. Presumably the Tegra hardware only supports > > > EHCI-1.0. > > > > I see, they're used for device addresses now. > > > > How can we make sure on Tegra systems we won't use those top two bits ? > > ehci-hcd doesn't use those device address bits at all. They are meant > for the LPM (Link Power Management) extension, which ehci-hcd doesn't > support. Even if support gets added in the future, we'll know that the > LPM capability isn't present unless bit 17 in the HCCPARAMS register is > set. > > On the other hand, what I wrote earlier about not overwriting those > bits wasn't quite correct. ehci-hcd _does_ overwrite them with 0's > during shutdown or removal. I don't know if this will matter for the > Tegra platform. This should not cause any issue to Tegra platform, as these bits are set during PHY power on. > > Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
