linux-kernel - Re: platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe

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Message-ID: <Zzs1rw1YcoEEeW7+@goliath>
Date: Mon, 18 Nov 2024 12:40:16 +0000
From: "Daniel Walker (danielwa)" <danielwa@...co.com>
To: Shinichiro Kawasaki <shinichiro.kawasaki@....com>
CC: Hans de Goede <hdegoede@...hat.com>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Ilpo J�rvinen
	<ilpo.jarvinen@...ux.intel.com>, Klara Modin <klarasmodin@...il.com>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, Danil Rybakov
	<danilrybakov249@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "xe-linux-external(mailer list)"
	<xe-linux-external@...co.com>
Subject: Re: platform/x86: p2sb: Allow p2sb_bar() calls during PCI device
 probe

On Mon, Nov 18, 2024 at 11:30:59AM +0000, Shinichiro Kawasaki wrote:
> 
> Thank you. Here I quote the relevant part of the debug log.
> 
> --------------------------------------------------------------------------------
> ...
> pci 0000:00:1f.0: [8086:19dc] type 00 class 0x060100 conventional PCI endpoint
> pci 0000:00:1f.1: [8086:19dd] type 00 class 0x058000 conventional PCI endpoint ... [A]
> pci 0000:00:1f.1: BAR 0 [mem 0xfd000000-0xfdffffff 64bit]
> pci 0000:00:1f.2: [8086:19de] type 00 class 0x058000 conventional PCI endpoint
> pci 0000:00:1f.2: BAR 0 [mem 0x88c00000-0x88c03fff]
> ...
> PCI: Using ACPI for IRQ routing
> pci 0000:00:1f.1: BAR 0 [mem 0xfd000000-0xfdffffff 64bit]: can't claim; no compatible bridge window ... [B]
> hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0, 0, 0, 0, 0, 0
> ...
> NET: Registered PF_XDP protocol family
> pci 0000:00:1f.1: BAR 0 [mem 0x280000000-0x280ffffff 64bit]: assigned ... [C]
> pci 0000:00:09.0: PCI bridge to [bus 01-06]
> ...
> PCI: CLS 64 bytes, default 64
> p2sb_cache_resources
> p2sb_cache_resources: P2SBC_HIDE=0  ... [D]
> p2sb_scan_and_cache_devfn: devfn=1f.1
> p2sb_scan_and_cache_devfn: 280000000-280ffffff: 140204 ... [E]
> PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> ...
> --------------------------------------------------------------------------------
> 
> Also, here I list my observations.
> 
> [A] The P2SB device was detected with DEVFN 1f.1, and device id 8086:19dd
> [B] Failed to claim its resource
> [C] Assigned new resource
> [D] p2sb_cache_resource() was called after the new resource assignment.
>     P2SBC_HIDE bit is not set.
> [E] The new resource was cached. IORESOURCE flags: MEM_64,SIZE_ALIGN,MEM.
> 
> So it was confirmed that the p2sb_cache_resource() was called after the new
> resource assignment, but Hans and Andy discuss that this order is not the
> problem cause, probably.
> 
> One thing I noticed is that p2sb_bar() call is not recorded in the log. My
> understanding is that all device drivers which use P2SB resource shouled call
> p2sb_bar(). Daniel, you noted that "a custom gpio device" disappeared. Does its
> device driver call p2sb_bar()?

No calls to p2sb_bar(). It maybe an Intel GPIO device actually. 0x8086 is Intel's vendor code.
I suspect it's something standard on Denverton.

> On the other hand, Daniel noted that,
> 
>   "The vendor and device details for the pci device are 8086:19dd."
> 
> I think 8086:19dd is the P2SB device itself. When p2sb_cache_resource() is
> called, pci_stop_and_remove_bus_device() is called for it, so I guess it is
> expected the device 8086:19dd disappears. Before applying the commit
> 5913320eb0b3, this pci_stop_and_remove_bus_device() call happened when
> p2sb_bar() was called. So, my mere guess is that Daniel's system's drivers do
> not call p2sb_bar() during the boot process, then the 8086:19dd P2SB device was
> still visible after boot.

The method I used for the bisect was to check lspci for 19dd. I find it odd that
the device which does exist was not in lspci. Also pci_get_device() fails for
this device and gpio operations can't happen.

Daniel