Mapping Physical Memory without a Device?

[Bruce M Simpson]

On Fri, Jun 06, 2003 at 01:30:28PM -0400, cd_freebsd wrote:
> I would like to be able to map memory before I have a device to work with (to read system BIOS information or mess with the video buffer). Is this possible? In linux, I would just call ioremap_nocache or request region. Is there a way to use bus_alloc_resource or something similar to accomplish this?

I assume you wish to do this from within the kernel.
The key ingredient here is pmap_kenter().

You would want to do something like this:

...
struct pcmem_softc {
        int                      sc_unit;
        device_t                 sc_dev;
        dev_t                    sc_cdev;
...
        /* common memory mapping descriptors */
        u_int32_t                sc_cm_base;
        int                      sc_cm_size;
        vm_offset_t              sc_cm_kva_base;
        u_int32_t                sc_cm_kva_size;
...
};

static vm_offset_t
pcmem_phys_map(struct pcmem_softc *sc)
{
        int              i;
        u_int32_t        off;
        u_int32_t        pa;
        vm_offset_t      va;
        vm_offset_t      size;

        /*
         * ensure the range to be mapped fits within page boundaries.
         */
        pa = round_page((u_int32_t) sc->sc_cm_base);
        sc->sc_cm_kva_size = size = round_page((u_int32_t) sc->sc_cm_size);
        off = (u_int32_t) sc->sc_cm_base - pa;
        /*
         * reserve a pageable memory range within the kva.
         */
        va = kmem_alloc_pageable(kernel_map, size);
        if (va == (vm_offset_t) 0)
                return (va);
        /*
         * wire each page into kva.
         */
        for (i = 0; i < size; i += PAGE_SIZE) {
                pmap_kenter(va + i, pa + i);
        }
#ifdef __i386__
        invltlb();
#endif
        return (va + off);
}

I wrote the above segment knowing much less about vm than I do now, so
it's probably too pmap and arch specific and could be done better.

Anything more elaborate (e.g. exporting pages to userland) would require
you to use a pager of type OBJT_PHYS.

BMS