On Tue, Nov 05, 2019 at 09:32:07PM +0000, Derrick, Jonathan wrote: > On Tue, 2019-11-05 at 10:12 +0000, Lorenzo Pieralisi wrote: > > On Mon, Nov 04, 2019 at 06:07:00PM +0000, Lorenzo Pieralisi wrote: > > > On Fri, Nov 01, 2019 at 10:16:39PM +0000, Derrick, Jonathan wrote: > > > > Hi Bjorn, > > > > > > > > On Fri, 2019-11-01 at 16:53 -0500, Bjorn Helgaas wrote: > > > > > [+cc Andrew] > > > > > > > > > > On Wed, Oct 16, 2019 at 11:04:47AM -0600, Jon Derrick wrote: > > > > > > When some VMDs are enabled and others are not, it's difficult to > > > > > > determine which IIO stack corresponds to the enabled VMD. > > > > > > > > > > > > To assist userspace with management tasks, VMD BIOS will write the VMD > > > > > > instance number and socket number into the first enabled root port's IO > > > > > > Base/Limit registers prior to OS handoff. VMD driver can capture this > > > > > > information and expose it to userspace. > > > > > > > > > > Hmmm, I'm not sure I understand this, but it sounds possibly fragile. > > > > > Are these Root Ports visible to the generic PCI core device > > > > > enumeration? If so, it will find them and read these I/O window > > > > > registers. Maybe today the PCI core doesn't change them, but I'm not > > > > > sure we should rely on them always being preserved until the vmd > > > > > driver can claim the device. > > > > > > > > > > > > > The Root Ports are on the VMD PCI domain, and this IO BASE/LIMIT > > > > parsing occurs before this PCI domain is exposed to the generic PCI > > > > scancode with pci_scan_child_bus(). Until that point the VMD PCI domain > > > > is invisible to the kernel outside of /dev/mem or resource0. > > > > > > That's because the VMD controller is a PCI device itself and its > > > BARs values are used to configure the VMD host controller. > > > > > > Interesting. > > > > > > To add to Bjorn's question, this reasoning assumes that whatever > > > code enumerates the PCI device representing the VMD host controller > > > does not overwrite its BARs upon bus enumeration otherwise the VMD > > > controller configuration would be lost. Am I reading the current > > > code correctly ? > > > > Sorry, I just went through the code again, I think the VMD controller > > PCI device BARs can and are allowed to be reassigned by the PCI > > enumeration code - I misread the code, so I raised a non-existent issue > > here, they are like any other PCI device MEM/IO BARs in this respect. > > > > Lorenzo > > > > Yes the VMD endpoint itself exposes the domain containing the Root > Ports. It's the Root Ports which get enumerated by generic PCI > scancode, and also the Root Port config space where this domain info is > supplied. Without a VMD driver, the only aperture to access the Root > Port config space is MMIO through the VMD endpoint's 'Config' BAR (aka > MEMBAR0). > > Without this patch, a /dev/mem, resource0, or third-party driver could > overwrite these values if they don't also restore them on close/unbind. > I imagine a kexec user would also overwrite these values. > > This is one of the reasons I was also thinking it could live in device > specific reset code as long as it can call into VMD for the specifics. > Many kernel vendors already ship with VMD=y, so I am tempted to simply > make that permanent and export a reset call to a dev specific reset in > quirks.c. Hi Jon, just wanted to ask you what's the plan with this series. Thanks, Lorenzo
