ioremap to a specific virtual address

[Nicolas Pitre]

On Fri, 23 Mar 2012, jonsmirl at gmail.com wrote:

> On Fri, Mar 23, 2012 at 12:00 AM, Nicolas Pitre <nico at fluxnic.net> wrote:
> > On Thu, 22 Mar 2012, jonsmirl at gmail.com wrote:
> >
> >> When iotable is used to initially map memory you can specify the
> >> mapping address. In this case IO_SDMMC_PHYS is 0x18000000 and it gets
> >> mapped to  0xf1800000
> >>
> >> NXP has supplied this handly macro
> >> #define io_p2v(x) (0xf0000000 | (((x) & 0xff000000) >> 4) | ((x) & 0x000fffff))
> >>
> >> iotable_init(lpc313x_io_desc, ARRAY_SIZE(lpc313x_io_desc));
> >>
> >>       {
> >>               .virtual        = io_p2v(IO_SDMMC_PHYS),
> >>               .pfn            = __phys_to_pfn(IO_SDMMC_PHYS),
> >>               .length         = IO_SDMMC_SIZE,
> >>               .type           = MT_DEVICE
> >>       },
> >>
> >> The supplied kernel is full of code that uses this type of addressing.
> >> It has macros for register definition that all depend on the registers
> >> being mapped to a well know location - io_p2v(x).
> >>
> >> I'd like to move the map out of the core code and into the SDMMC
> >> device driver and then only do it if the driver loads.
> >
> > Why would you do that?  Those static mappings are meant to be global and
> > remain there.  The handy macro is in fact not handy at all as it forces
> > virtual addresses on you.
> 
> I'm ok with global static mappings. What I'd like to do is build the
> static iotable from the device tree instead of repeating every device
> in the map_desc array. I suppose I could dynamically allocate it, fill
> it in from the device tree and call iotable_init().

Well, if you have a device tree with that stuff, then you may as well 
just forget about the static mappings.

> What is the right way to make the initial static mappings?

Typically by declaring it in the code.  Otherwise there is some 
infrastructure already in place for drivers to map their hardware 
dynamically from DT information.


Nicolas