Re: [PATCH v6 4/5] PCI: vmd: Update type of the __iomem pointers

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Nov 30, 2020 at 09:06:56AM +0000, David Laight wrote:
> From: Krzysztof Wilczynski
> > Sent: 29 November 2020 23:08
> > 
> > Use "void __iomem" instead "char __iomem" pointer type when working with
> > the accessor functions (with names like readb() or writel(), etc.) to
> > better match a given accessor function signature where commonly the
> > address pointing to an I/O memory region would be a "void __iomem"
> > pointer.
> 
> ISTM that is heading in the wrong direction.
> 
> I think (form the variable names etc) that these are pointers
> to specific registers.
> 
> So what you ought to have is a type for that register block.
> Typically this is actually a structure - to give some type
> checking that the offsets are being used with the correct
> base address.

In this case, "cfgbar" is not really a pointer to a register; it's the
address of memory-mapped config space.  The VMD hardware turns
accesses to that space into PCI config transactions on its secondary
side.  xgene_pcie_get_cfg_base() and brcm_pcie_map_conf() are similar
situations and use "void *".

Bjorn