Re: [RFC Patch V1] ioatdma: Ignore IOAT devices under hotplug-capable PCI host bridge

[Jiang Liu <jiang.liu@linux.intel.com>]

Hi Dave,
	Gentle Ping:) Any suggestion about this patch?
Thanks!
Gerry
On 2015/6/2 14:36, Jiang Liu wrote:
> The dmaengine core assumes that async DMA devices will only be removed
> when they not used anymore, or it assumes dma_async_device_unregister()
> will only be called by dma driver exit routines. But this assumption is
> not true for the IOAT driver, which calls dma_async_device_unregister()
> from ioat_remove(). So current IOAT driver doesn't support device
> hot-removal because it may cause system crash to hot-remove an inuse
> IOAT device.
> 
> To support CPU socket hot-removal, all PCI devices, including IOAT
> devices embedded in the socket, will be hot-removed. The idea solution
> is to enhance the dmaengine core and IOAT driver to support hot-removal,
> but that's too hard.
> 
> This patch implements a hack to disable IOAT devices under hotplug-capable
> CPU socket so it won't break socket hot-removal.
> 
> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
> ---
>  drivers/dma/ioat/pci.c |   34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/drivers/dma/ioat/pci.c b/drivers/dma/ioat/pci.c
> index 76f0dc688a19..3b8c9b03f4b3 100644
> --- a/drivers/dma/ioat/pci.c
> +++ b/drivers/dma/ioat/pci.c
> @@ -27,6 +27,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/dca.h>
>  #include <linux/slab.h>
> +#include <linux/acpi.h>
>  #include "dma.h"
>  #include "dma_v2.h"
>  #include "registers.h"
> @@ -148,6 +149,34 @@ alloc_ioatdma(struct pci_dev *pdev, void __iomem *iobase)
>  	return d;
>  }
>  
> +/*
> + * The dmaengine core assumes that async DMA devices will only be removed
> + * when they not used anymore, or it assumes dma_async_device_unregister()
> + * will only be called by dma driver exit routines. But this assumption is
> + * not true for the IOAT driver, which calls dma_async_device_unregister()
> + * from ioat_remove(). So current IOAT driver doesn't support device
> + * hot-removal because it may cause system crash to hot-remove inuse IOAT
> + * devices.
> + *
> + * This is a hack to disable IOAT devices under ejectable PCI host bridge
> + * so it won't break PCI host bridge hot-removal.
> + */
> +static bool ioat_pci_has_ejectable_acpi_ancestor(struct pci_dev *pdev)
> +{
> +#ifdef CONFIG_ACPI
> +	struct pci_bus *bus = pdev->bus;
> +	struct acpi_device *adev;
> +
> +	while (bus->parent)
> +		bus = bus->parent;
> +	for (adev = ACPI_COMPANION(bus->bridge); adev; adev = adev->parent)
> +		if (adev->flags.ejectable)
> +			return true;
> +#endif
> +
> +	return false;
> +}
> +
>  static int ioat_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  {
>  	void __iomem * const *iomap;
> @@ -155,6 +184,11 @@ static int ioat_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	struct ioatdma_device *device;
>  	int err;
>  
> +	if (ioat_pci_has_ejectable_acpi_ancestor(pdev)) {
> +		dev_dbg(&pdev->dev, "ignore ejectable IOAT device.\n");
> +		return -ENODEV;
> +	}
> +
>  	err = pcim_enable_device(pdev);
>  	if (err)
>  		return err;
>