On Wed, 2 Jul 2014, Stephen Warren wrote: > On 07/02/2014 10:09 AM, Alan Stern wrote: > > On Wed, 2 Jul 2014, Stephen Warren wrote: > > > >> On 07/02/2014 08:02 AM, Alan Stern wrote: > >>> On Wed, 2 Jul 2014, Tuomas Tynkkynen wrote: > >>> > >>>> Hi all, > >>>> > >>>> This series fixes a probe order issue with the Tegra EHCI driver. > >>>> Basically, the register area of the 1st USB controller contains some > >>>> registers that are global to all of the controllers, but that are also > >>>> cleared when reset is asserted to the 1st controller. So if (say) the > >>>> 3rd controller would be the first one to finish probing successfully, > >>>> then the reset that happens during the 1st controller's probe would > >>>> result in broken USB. So the before doing anything with the USB HW, > >>>> we should reset the 1st controller once, and then never ever reset > >>>> it again. > >>> > >>> This sounds very much like the sort of thing that ought to be described > >>> in DT. It is a hardware dependence, and DT exists for the purpose of > >>> describing the hardware. > >> > >> DT is more about describing the HW, not how SW has to use the HW. > > > > Tuomas wrote: "the register area of the 1st USB controller contains > > some registers that are global to all of the controllers, but that are > > also cleared when reset is asserted to the 1st controller." That is > > very much an attribute of the hardware and so DT should describe it. > > So you want to add a Boolean DT property to the first USB controller > node indicating that it has the "shared" reset? Something like that, yes. > That would be fine, but > would only replace the content of tegra_find_usb1_node(); much of the > rest of the patch would remain the same. That's okay. tegra_find_usb1_node() was the most objectionable part of the patch. > I guess in this case, it's fine to require DT changes to enable the new > feature of fixing this issue, so long as the code continues to work the > same as it currently does with old DTs. Due to the backwards > compatibility requirement, the patch will end up slightly more complex, > but hopefully not too bad. Good. 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
