Re: [PATCH v1 1/3] PCI: export pci_get_dma_device() helper to other users

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Fri, 2014-07-25 at 10:58 -0600, Alex Williamson wrote:
> On Fri, 2014-07-25 at 16:31 +0300, Andy Shevchenko wrote:
> > Some chipsets use the function 0 for DMA on other functions of a
> > multifunctional device. One of the example is Intel EG20T PCH. This is also
> > applicable to Lynxpoint PCH when LPSS devices are switched to PCI mode.
> > 
> > This patch exports a useful helper to get a device of the DMA. This device is
> > needed to request a DMA channel from a proper controller.
> > 
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/pci/quirks.c | 2 +-
> >  include/linux/pci.h  | 9 +++++++++
> >  2 files changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 80c2d01..8352e5b 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -3517,7 +3517,7 @@ static struct pci_dev *pci_func_0_dma_source(struct pci_dev *dev)
> >  	if (!PCI_FUNC(dev->devfn))
> >  		return pci_dev_get(dev);
> >  
> > -	return pci_get_slot(dev->bus, PCI_DEVFN(PCI_SLOT(dev->devfn), 0));
> > +	return pci_get_dma_device(dev);
> >  }
> >  
> >  static const struct pci_dev_dma_source {
> > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > index 61978a4..86caab7 100644
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1575,6 +1575,15 @@ static inline int pci_dev_specific_acs_enabled(struct pci_dev *dev,
> >  static inline void pci_dev_specific_enable_acs(struct pci_dev *dev) { }
> >  #endif
> >  
> > +/*
> > + * Some chipsets use the function 0 for DMA on other functions of a
> > + * multifunctional device.
> > + */
> > +static inline struct pci_dev *pci_get_dma_device(struct pci_dev *dev)
> > +{
> > +	return pci_get_slot(dev->bus, PCI_DEVFN(PCI_SLOT(dev->devfn), 0));
> > +}
> > +
> >  void __iomem *pcim_iomap(struct pci_dev *pdev, int bar, unsigned long maxlen);
> >  void pcim_iounmap(struct pci_dev *pdev, void __iomem *addr);
> >  void __iomem * const *pcim_iomap_table(struct pci_dev *pdev);
> 
> You've created a very generic function for a very specific problem.  I
> can't just call this on any random device and expect it to work
> correctly.

Right.

>   What about all the other device which use function 1 for
> their DMA alias.

Hmm... I would like to understand what the difference between DMA alias
and the case when we have MFD where function 0 is real DMA controller
which serves the other devices in that block is?

Another (probably minor) question, why do you still have
pci_get_dma_source() function in quirks.c?

>   We've just added infrastructure in PCI to support DMA
> aliases, see pci_for_each_dma_alias().  Please use this instead.  Quirks
> can be added to set the dma_alias_devfn and
> PCI_DEV_FLAGS_DMA_ALIAS_DEVFN to indicate that it's valid.  Thanks,

Do you mean I have to list all devices that, for example, are listed in
the spi-topcliff-pch.c?


-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
Intel Finland Oy

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