Date:	Thu, 19 May 2016 14:49:30 +0000
From:	"Jiang, Dave" <dave.jiang@...el.com>
To:	Gavin Guo <gavin.guo@...onical.com>
CC:	"Koul, Vinod" <vinod.koul@...el.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>
Subject: RE: ioatdma(Intel(R) I/OAT DMA Engine init failed)

> -----Original Message-----
> From: Gavin Guo [mailto:gavin.guo@...onical.com]
> Sent: Wednesday, May 18, 2016 8:19 PM
> To: Jiang, Dave <dave.jiang@...el.com>
> Cc: Koul, Vinod <vinod.koul@...el.com>; dmaengine@...r.kernel.org; linux-kernel@...r.kernel.org; Williams, Dan J
> <dan.j.williams@...el.com>
> Subject: Re: ioatdma(Intel(R) I/OAT DMA Engine init failed)
> 
> On Thu, May 19, 2016 at 12:49 AM, Jiang, Dave <dave.jiang@...el.com> wrote:
> > On Wed, 2016-05-18 at 13:27 +0000, Gavin Guo wrote:
> >> On Tue, May 17, 2016 at 6:06 PM, Vinod Koul <vinod.koul@...el.com>
> >> wrote:
> >> >
> >> > On Mon, May 16, 2016 at 06:08:20PM +0800, Gavin Guo wrote:
> >> > >
> >> > > The following error messages can be observed on the Intel
> >> > > Haswell-E
> >> > > chipset with v3.13 kernel. After the analysis, I found there is
> >> > > no
> >> > > difference in the logic of these error messages in the current
> >> > > upstream kernel. I also searched the git log and can't find any
> >> > > commit
> >> > > which is fix to the error(correct me if I am wrong). The
> >> > > following is
> >> > > the detail, and I'll really appreciate if there is any comment.
> >> > > :)
> >> > 3.13 is ancient, can you check this on latest kernel
> >> Thank you for the comment. It's running on the production system.
> >> However,
> >> I'll try to figure out if it's possible to test the latest kernel.
> >
> > I wonder if you don't have the extended PCI config space access enabled
> > in your kernel config.
> 
> Really thanks for your advice. :)
> 
> I searched the internet about the extended PCI config space and found
> the link:
> 
> [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in
> http://lwn.net/Articles/263288/

Can you try calling pci_enable_ext_config() in the PCI probe for your kernel? I just haven't seen this issue in the latest kernel. 

> 
> And I checked the config and found the CONFIG_PCI_MMCONFIG=y. The
> following string also can be observed in the dmesg:
> 
> [    1.419853] PCI: MMCONFIG for domain 0000 [bus 00-ff] at
> [mem0x80000000-0x8fffffff] (base 0x80000000)
> [    1.419855] PCI: MMCONFIG at [mem 0x80000000-0x8fffffff] reserved in E820
> 
> It seems the extended PCI config space is enabled. If there is
> anything missed?
> 
> >
> >>
> >> >
> >> >
> >> > >
> >> > >
> >> > > ioatdma 0000:00:04.0: channel error register unreachable
> >> > > ioatdma 0000:00:04.0: channel enumeration error
> >> > > ioatdma 0000:00:04.0: Intel(R) I/OAT DMA Engine init failed
> >> > > ioatdma 0000:00:04.1: channel error register unreachable
> >> > > ioatdma 0000:00:04.1: channel enumeration error
> >> > > ioatdma 0000:00:04.1: Intel(R) I/OAT DMA Engine init failed
> >> > > ...
> >> > > ioatdma 0000:00:04.7: channel error register unreachable
> >> > > ioatdma 0000:00:04.7: channel enumeration error
> >> > > ioatdma 0000:00:04.7: Intel(R) I/OAT DMA Engine init failed
> >> > > mei_me 0000:00:16.0: initialization failed.
> >> > >
> >> > > There are 8 I/OAT DMA controllers on the Haswell-E chipset:
> >> > > 8086:2f20 ~ 8086:2f27
> >> > > 80:04.0 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 0 (rev 02)
> >> > > 80:04.1 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 1 (rev 02)
> >> > > 80:04.2 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 2 (rev 02)
> >> > > 80:04.3 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 3 (rev 02)
> >> > > 80:04.4 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 4 (rev 02)
> >> > > 80:04.5 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 5 (rev 02)
> >> > > 80:04.6 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 6 (rev 02)
> >> > > 80:04.7 System peripheral: Intel Corporation Haswell-E DMA
> >> > > Channel 7 (rev 02)
> >> > >
> >> > > Analysis:
> >> > > The bug happens when the driver is resetting DMA controller, this
> >> > > is
> >> > > the sequence: The function, ioat_pci_probe, is called when the
> >> > > DMA
> >> > > controller is detected by the PCI bus. Then,
> >> > > ioat3_dma_probe -> ioat_probe -> ioat2_enumerate_channels ->
> >> > > ioat3_reset_hw. The following code can be found in the
> >> > > ioat3_reset_hw:
> >> > >
> >> > > drivers/dma/ioat/dma_v3.c:
> >> > >         chanerr = readl(chan->reg_base + IOAT_CHANERR_OFFSET);
> >> > >         writel(chanerr, chan->reg_base + IOAT_CHANERR_OFFSET);
> >> > > ...
> >> > >         err = pci_read_config_dword(pdev,
> >> > > IOAT_PCI_CHANERR_INT_OFFSET, &chanerr);
> >> > > if (err) {
> >> > > dev_err(&pdev->dev,
> >> > > "channel error register unreachable\n");
> >> > > return err;
> >> > > }
> >> > >
> >> > > Obviously, there are something wrong in the channel error
> >> > > register
> >> > > reset process. Then all the way back to ioat_probe(). Because the
> >> > > error happens, the dma->chancnt will be set to 0:
> >> > >
> >> > > drivers/dma/ioat/dma.c:
> >> > >         if (!dma->chancnt) {
> >> > >                 dev_err(dev, "channel enumeration error\n");
> >> > >                 goto err_setup_interrupts;
> >> > >         }
> >> > >
> >> > > Finally back to ioat_pci_probe:
> >> > >
> >> > > drivers/dma/ioat/pci.c:
> >> > >                 err = ioat3_dma_probe(device, ioat_dca_enabled);
> >> > >         else
> >> > >                 return -ENODEV;
> >> > >
> >> > >         if (err) {
> >> > >                 dev_err(dev, "Intel(R) I/OAT DMA Engine init
> >> > > failed\n");
> >> > >                 return -ENODEV;
> >> > --
> >> > ~Vinod

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