On Monday, March 31, 2014 at 12:38:01 PM, Lucas Stach wrote: > Am Montag, den 31.03.2014, 11:36 +0200 schrieb Marek Vasut: > > On Monday, March 31, 2014 at 11:28:29 AM, Lucas Stach wrote: > > > Am Sonntag, den 30.03.2014, 19:36 +0200 schrieb Marek Vasut: > > > > On Friday, March 28, 2014 at 05:52:53 PM, Lucas Stach wrote: > > > > > The glue around the core designware IP is significantly > > > > > different between the Exynos and i.MX implementation, > > > > > which is reflected in the DT bindings. > > > > > > > > > > This changes the i.MX6 binding to reuse as much as > > > > > possible from the common designware binding and > > > > > removes old cruft. > > > > > > > > > > I removed the optional GPIOs with the following reasoning: > > > > > - disable-gpio: endpoint specific GPIO, not currently > > > > > > > > > > wired up in any code. Should be handled by the PCI device > > > > > driver, not the host controller driver. > > > > > > > > > > - wake-up-gpio: same as above. > > > > > - power-on-gpio: No user in any upstream DT. This should > > > > > > > > > > be handled by a regulator which shouldn't be controlled > > > > > by the host driver, but rather by the PCI device driver. > > > > > > > > This power-on-gpio should indeed be handled by the regulator, but the > > > > regulator cannot be handled by the PCIe device driver. This > > > > power-on-gpio must be operated on per-slot basis if I understand it > > > > correctly, so it cannot be controlled by the host controller driver > > > > either. > > > > > > > > The reason why this cannot be controlled by the device driver is that > > > > if the device is powered down, it won't be detected on the PCIe bus, > > > > thus it cannot enable the regulator which will power up the slot the > > > > device is sitting in. > > > > > > So we are on the same page with regard to a GPIO being the wrong > > > abstraction for this, I think. > > > > Yes. > > > > > For the regulator part I would argue that PCI is a bus that is built > > > around the ability to inspect the bus and detect devices on the bus at > > > probe time, so any regulator that's powering a PCI device should be > > > boot-on. > > > > This thing about regulator being boot-on should really be documented. > > > > Moreover, I think it's a waste of power to keep the devices ON on boot > > even if the PCIe bus was not started (yet). The bus might not be started > > at all and the regulators would still be ON, which would be quite a > > waste. > > It's the exact same behavior that you get on x86: all devices are > powered after boot, once you loaded a device driver it may choose to > turn the device off. I don't think it makes sense to deviate here for > the sake of being embedded and special. > > > > Only after the device driver is loaded it should be able to fetch the > > > regulator to power down/up the device as it wishes. In the x86 world > > > this is AFAIK done using ACPI methods. > > > > > > I think the host controller driver has no business in controlling the > > > device power, more so as there possibly could be a lot of devices on > > > the bus even with a single host lane. > > > > The power should be controlled per-slot, but I don't know how to model > > that. Note that there might be a PCIe device with a switch popped into a > > single slot, which makes things much more interesting. In such case, you > > need to power up the slot and neither of the downstream devices should > > control the power regulator of that slot. > > We could just add the regulator to the PCI hierarchy in the DT and > handle it similar to IRQs where we just walk up the DT starting from the > device until we find the matching IRQ/regulator. > > Still for this to work with a regulator shared between several devices, > all the device drivers have to be aware of the regulator. Otherwise a > single device may choose to power down and erroneously cut power to a > sibling device, where the driver hasn't requested the regulator. > > In all those scenarios the host controller driver still would not have > any business dealing with the regulator. Same situation as with the > legacy IRQs, that aren't handled by the host driver, but just routed to > the right instance through the DT. OK, it all makes sense. What I find a bit unfortunate is that we loose the Plug- n-Play nature of the PCIe here, but I guess that cannot be helped. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
