ioatdma(Intel(R) I/OAT DMA Engine init failed)

[Gavin Guo]

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. :)

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;