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

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Date:	Mon, 8 Jun 2015 16:12:34 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Dave Jiang <dave.jiang@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	David Woodhouse <dwmw2@...radead.org>,
	Tony Luck <tony.luck@...el.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [RFC Patch V1] ioatdma: Ignore IOAT devices under
 hotplug-capable PCI host bridge

On Tue, Jun 02, 2015 at 02:37:31PM +0800, Jiang Liu wrote:
> Ccing Rafael, it's ACPI hotplug related.
> 
> 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.
> > 
So below looks okay though I wonder how hard would it be to fix hot unplug ?

-- 
~Vinod

> > Signed-off-by: Jiang Liu <jiang.liu@...ux.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;
> > 

-- 
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