[lkml]   [2020]   [Jul]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected
On Friday 10 July 2020 10:18:00 Lorenzo Pieralisi wrote:
> On Thu, Jul 09, 2020 at 05:09:59PM +0200, Pali Rohár wrote:
> > > I understand that but the bridge bus resource can be trimmed to just
> > > contain the root bus because that's the only one where there is a
> > > chance you can enumerate a device.
> >
> > It is possible to register only root bridge without endpoint?
> It is possible to register the root bridge with a trimmed IORESOURCE_BUS
> so that you don't enumerate anything other than the root port.

Hello Lorenzo! I really do not know how to achieve it. From code it
looks like that pci/probe.c scans child buses unconditionally.

pci-aardvark.c calls pci_host_probe() which calls functions
pci_scan_root_bus_bridge() which calls pci_scan_child_bus() which calls
pci_scan_child_bus_extend() which calls pci_scan_bridge_extend() (bridge
needs to be reconfigured) which then try to probe child bus via
pci_scan_child_bus_extend() because bridge is not card bus.

In function pci_scan_bridge_extend() I do not see a way how to skip
probing for child buses which would avoid enumerating aardvark root
bridge when PCIe device is not connected.

dmesg output contains:

advk-pcie d0070000.pcie: link never came up
advk-pcie d0070000.pcie: PCI host bridge to bus 0000:00
pci_bus 0000:00: root bus resource [bus 00-ff]
pci_bus 0000:00: root bus resource [mem 0xe8000000-0xe8ffffff]
pci_bus 0000:00: root bus resource [io 0x0000-0xffff] (bus address [0xe9000000-0xe900ffff])
pci_bus 0000:00: scanning bus
pci 0000:00:00.0: [1b4b:0100] type 01 class 0x060400
pci 0000:00:00.0: reg 0x38: [mem 0x00000000-0x000007ff pref]
pci_bus 0000:00: fixups for bus
pci 0000:00:00.0: scanning [bus 00-00] behind bridge, pass 0
pci 0000:00:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
pci 0000:00:00.0: scanning [bus 00-00] behind bridge, pass 1
pci_bus 0000:01: scanning bus
advk-pcie d0070000.pcie: advk_pcie_valid_device

 \ /
  Last update: 2020-07-13 10:28    [W:0.213 / U:0.144 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site