Re: [RFC PATCH 1/2] common: dma-mapping: introduce dma_get_parent_cfg() helper

[Murali Karicheri]

On 12/17/2014 07:09 PM, Arnd Bergmann wrote:
> On Wednesday 17 December 2014 18:24:43 Murali Karicheri wrote:
> > On 12/17/2014 04:56 PM, Arnd Bergmann wrote:
> > > On Wednesday 17 December 2014 13:02:23 Murali Karicheri wrote:
> > >
> > > What's wrong with using arch_setup_dma_ops() from PCI as suggested
> > > previously?
>
> +Will Deacon
>
> > I had originally written a code based on that line as below. But
> > dma-ranges property is also used by ppc and other architectures in the
> > pci device DT node. So I wasn't sure how this code impact PCI driver
> > functionality on those platforms. Hence used a simpler change as all
> > that is needed for keystone is to get the dma_pfn_offset rightly set in
> > the pci slave device.
>
> But in your patch, you don't call arch_setup_dma_ops() at all.
>
> > Initially I had a function implemented as below for this in of_pci.c.
> >
> > + * of_pci_dma_configure - Setup DMA configuration for a pci device
> > + * @dev:       pci device to apply DMA configuration
> > + *
> > + * Try to get devices's DMA configuration from DT and update it
> > + * accordingly. This is a similar to of_dma_configure() for platform
> > + * devices.
> > + *
> > + */
> > +void of_pci_dma_configure(struct pci_dev *dev)
> > +{
> > +       struct device *host_bridge, *parent;
> > +       struct pci_bus *bus = dev->bus;
> > +       u64 dma_addr, paddr, size;
> > +       int ret;
> > +
> > +       while (!pci_is_root_bus(bus))
> > +               bus = bus->parent;
> > +       host_bridge = bus->bridge;
> > +
> > +       parent = host_bridge->parent;
> > +       if (parent->of_node) {
>
> so far it looks good, although we may want to introduce
> a helper function to get the of_node.

Will add

> > +               /*
> > +                * if dma-coherent property exist, call arch hook to setup
> > +                * dma coherent operations.
> > +                */
> > +               if (of_dma_is_coherent(parent->of_node)) {
> > +                       set_arch_dma_coherent_ops(&dev->dev);
> > +                       dev_info(&dev->dev, "device is dma coherent\n");
> > +               }
>
> set_arch_dma_coherent_ops no longer exists. Just keep the flag in a
> local variable

Ok.

> > +               /*
> > +                * if dma-ranges property doesn't exist - just return else
> > +                * setup the dma offset
> > +                */
> > +               ret = of_dma_get_range(parent->of_node,&dma_addr,
> > &paddr,&size);
> > +               if (ret<  0) {
> > +                       dev_info(&dev->dev, "no dma range information to
> > setup\n");
> > +                       printk("no dma range information to setup\n");
> > +                       return;
> > +               }
> > +
> > +               /* DMA ranges found. Calculate and set dma_pfn_offset */
> > +               dev->dev.dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
> > +               dev_info(&dev->dev, "dma_pfn_offset(%#08lx)\n",
> > dev->dev.dma_pfn_offset);
>
> Same for the offset and size here, then pass all of the above into
> arch_setup_dma_ops. This is also where we need to hook up the iommu
> support once we decide how to make that work with the ARM SMMU.

Ok. I will make this similar to of_dma_configure() that can be called 
from pci/probe.c

Murali
> Will, I think we may have a problem on ARM64 now, since we only replaced
> set_arch_dma_coherent_ops on ARM32 but not ARM64. Can you send a fix for
> this? Without that, we don't have any coherent operations on ARM64 any
> more, unless I'm missing something.
>
> 	Arnd
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--
Murali Karicheri
Linux Kernel, Texas Instruments
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