Re: [PATCH] PCI: Clear PCI_STATUS when setting up the device

From: Bjorn Helgaas <helgaas@kernel.org>
To: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: Christophe Fergeau <cfergeau@redhat.com>,
	bhelgaas@google.com, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI: Clear PCI_STATUS when setting up the device
Date: Fri, 4 Nov 2022 10:53:39 -0500	[thread overview]
Message-ID: <20221104155339.GA95864@bhelgaas> (raw)
In-Reply-To: <20220517043738.2308499-1-kai.heng.feng@canonical.com>

On Tue, May 17, 2022 at 12:37:38PM +0800, Kai-Heng Feng wrote:
> We are seeing Master Abort bit is set on Intel I350 ethernet device and its
> root port right after boot, probably happened during BIOS phase:
> 
> 00:06.0 PCI bridge [0604]: Intel Corporation Device [8086:464d] (rev 05) (prog-if 00 [Normal decode])
>         Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort+ >SERR- <PERR- INTx-
> 
> 6e:00.0 Ethernet controller [0200]: Intel Corporation I350 Gigabit Network Connection [8086:1521] (rev 01)
>         Subsystem: Intel Corporation Ethernet Server Adapter I350-T2 [8086:00a2]
>         Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort+ >SERR- <PERR- INTx-
> 
> 6e:00.1 Ethernet controller [0200]: Intel Corporation I350 Gigabit Network Connection [8086:1521] (rev 01)
>         Subsystem: Intel Corporation Ethernet Server Adapter I350-T2 [8086:00a2]
>         Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort+ >SERR- <PERR- INTx-
> 
> And the Master Abort bit is cleared after S3.
> 
> Since there's no functional impact found, clear the PCI_STATUS to treat
> it anew at setting up.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=215989
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>

This patch appeared in v6.0 as 6cd514e58f12 ("PCI: Clear PCI_STATUS
when setting up device").  Christophe reported in the bugzilla that it
causes boot failures:

> --- Comment #3 from Christophe Fergeau (cfergeau@redhat.com) ---
> This commit
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6c
> d514e58f12b211d638dbf6f791fa18d854f09c
> references this issue.
> This commit causes boot failures when trying to start linux guests with Apple's
> hypervisor framework (for example using https://github.com/evansm7/vftool ).
> After reverting it, I can successfully boot 6.1-rc kernels on my macOS12 x86_64
> macbook. With this commit, the VM fails to start, additional details in
> https://bugzilla.redhat.com/show_bug.cgi?id=2137803

> ---
>  drivers/pci/probe.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d370..414f659dc8735 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1890,6 +1890,9 @@ int pci_setup_device(struct pci_dev *dev)
>  
>  	dev->broken_intx_masking = pci_intx_mask_broken(dev);
>  
> +	/* Clear errors left from system firmware */
> +	pci_write_config_word(dev, PCI_STATUS, 0xffff);
> +
>  	switch (dev->hdr_type) {		    /* header type */
>  	case PCI_HEADER_TYPE_NORMAL:		    /* standard header */
>  		if (class == PCI_CLASS_BRIDGE_PCI)
> -- 
> 2.34.1
> 