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
>
> 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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