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From: "Pali Rohár" <pali@kernel.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: "Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	Xogium <contact@xogium.me>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Mon, 13 Jul 2020 10:27:47 +0200	[thread overview]
Message-ID: <20200713082747.e3q3ml3wpbszn4j7@pali> (raw)
In-Reply-To: <20200710091800.GA3419@e121166-lin.cambridge.arm.com>

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

WARNING: multiple messages have this Message-ID
From: "Pali Rohár" <pali@kernel.org>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: "Tomasz Maciej Nowak" <tmn505@gmail.com>,
	linux-pci@vger.kernel.org, Xogium <contact@xogium.me>,
	linux-kernel@vger.kernel.org, "Marek Behún" <marek.behun@nic.cz>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	linux-arm-kernel@lists.infradead.org,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>
Subject: Re: [PATCH v3] PCI: aardvark: Don't touch PCIe registers if no card connected
Date: Mon, 13 Jul 2020 10:27:47 +0200	[thread overview]
Message-ID: <20200713082747.e3q3ml3wpbszn4j7@pali> (raw)
In-Reply-To: <20200710091800.GA3419@e121166-lin.cambridge.arm.com>

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

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  parent reply	other threads:[~2020-07-13  8:27 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 14:31 [PATCH] " Pali Rohár
2020-05-28 14:31 ` Pali Rohár
2020-05-28 16:26 ` Bjorn Helgaas
2020-05-28 16:26   ` Bjorn Helgaas
2020-05-28 16:38   ` Pali Rohár
2020-05-28 16:38     ` Pali Rohár
2020-05-28 16:49     ` Bjorn Helgaas
2020-05-28 16:49       ` Bjorn Helgaas
2020-05-29  8:30       ` Pali Rohár
2020-05-29  8:30         ` Pali Rohár
2020-06-30 12:31         ` Pali Rohár
2020-06-30 12:31           ` Pali Rohár
2020-06-30 13:51     ` Bjorn Helgaas
2020-06-30 13:51       ` Bjorn Helgaas
2020-06-30 14:04       ` Pali Rohár
2020-06-30 14:04         ` Pali Rohár
2020-06-30 14:58         ` Bjorn Helgaas
2020-06-30 14:58           ` Bjorn Helgaas
2020-07-01  8:08           ` Pali Rohár
2020-07-01  8:08             ` Pali Rohár
2020-07-01  8:20 ` [PATCH v2] " Pali Rohár
2020-07-01  8:20   ` Pali Rohár
2020-07-01 21:34   ` Bjorn Helgaas
2020-07-01 21:34     ` Bjorn Helgaas
2020-07-02  8:23     ` Pali Rohár
2020-07-02  8:23       ` Pali Rohár
2020-07-02  8:30 ` [PATCH v3] " Pali Rohár
2020-07-02  8:30   ` Pali Rohár
2020-07-09 11:35   ` Lorenzo Pieralisi
2020-07-09 11:35     ` Lorenzo Pieralisi
2020-07-09 12:22     ` Pali Rohár
2020-07-09 12:22       ` Pali Rohár
2020-07-09 14:47       ` Lorenzo Pieralisi
2020-07-09 14:47         ` Lorenzo Pieralisi
2020-07-09 15:09         ` Pali Rohár
2020-07-09 15:09           ` Pali Rohár
2020-07-10  9:18           ` Lorenzo Pieralisi
2020-07-10  9:18             ` Lorenzo Pieralisi
2020-07-10 15:44             ` Pali Rohár
2020-07-10 15:44               ` Pali Rohár
2020-07-10 16:08               ` Bjorn Helgaas
2020-07-10 16:08                 ` Bjorn Helgaas
2020-07-10 19:30                 ` Pali Rohár
2020-07-10 19:30                   ` Pali Rohár
2020-07-10 20:08                   ` Bjorn Helgaas
2020-07-10 20:08                     ` Bjorn Helgaas
2020-07-13  8:27             ` Pali Rohár [this message]
2020-07-13  8:27               ` Pali Rohár
2020-07-13 11:23               ` Lorenzo Pieralisi
2020-07-13 11:23                 ` Lorenzo Pieralisi
2020-07-13 14:50                 ` Pali Rohár
2020-07-13 14:50                   ` Pali Rohár
2020-07-13 16:41                   ` Lorenzo Pieralisi
2020-07-13 16:41                     ` Lorenzo Pieralisi
2020-07-14  7:38                     ` Pali Rohár
2020-07-14  7:38                       ` Pali Rohár
2020-07-15 12:17                 ` Pali Rohár
2020-07-15 12:17                   ` Pali Rohár
2020-07-15 16:21                   ` Lorenzo Pieralisi
2020-07-15 16:21                     ` Lorenzo Pieralisi
2020-07-21  8:57                     ` Pali Rohár
2020-07-21  8:57                       ` Pali Rohár
2020-07-21 10:48                       ` Lorenzo Pieralisi
2020-07-21 10:48                         ` Lorenzo Pieralisi

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