Re: RFC: being more anal about iospace accesses..

[Matthew Wilcox <willy@debian.org>]

On Wed, Sep 15, 2004 at 06:38:50PM -0400, James Bottomley wrote:
> Please can we not do it this way, that was the old pci_map_single et al
> which we've just spent quite a bit of time converting to
> dma_map_single.  It might not matter to the PCI centric people, but the
> generic DMA API was a wonderful simplification to the rest of us.
> 
> Can we start iomap off on the right foot and simply do dma_iomap (or
> dev_iomap since dma_ may end up to be confusing), taking a struct device
> as an argument and let the platform, which knows where the buses are,
> map this to the correct operations?

Actually, I think we're OK with the current interface here.  The routines
we have that give us an iomem pointer are:

/* Create a virtual mapping cookie for an IO port range */
extern void __iomem *ioport_map(unsigned long port, unsigned int nr);
extern void ioport_unmap(void __iomem *);

/* Create a virtual mapping cookie for a PCI BAR (memory or IO) */
struct pci_dev;
extern void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max);
extern void pci_iounmap(struct pci_dev *dev, void __iomem *);

So rather than pass the struct device in, we've got a special function
for each bus type.


What we haven't dealt with in this interface are:

 - relaxed reads
 - byte ordering

The relaxed attribute is, I think, not a property of the space we're
looking at.  It's a property of any given transaction.  So I think we
really do want a set of ioreadXX_relaxed() functions.

Byte ordering I'm less clear on.  Is this a property of the area "this
area is little endian on the bus, but the host cpu is big endian",
or is it a property of an individual transaction?

-- 
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the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince 
himself that the war is just, and will thank God for the better sleep 
he enjoys after this process of grotesque self-deception." -- Mark Twain