Re: [PATCH 05/14] lib: Add I/O map cache implementation

[Thierry Reding]

On Thu, Jan 10, 2013 at 12:24:17PM -0700, Jason Gunthorpe wrote:
> On Thu, Jan 10, 2013 at 08:03:27PM +0100, Thierry Reding wrote:
> 
> > > > You'd piece a mapping together, each bus requires 16 64k mappings, a
> > > > simple 2d array of busnr*16 of pointers would do the trick. A more
> > > > clever solution would be to allocate contiguous virtual memory and
> > > > split that up..
>  
> > > Oh, I see. I'm not very familiar with the internals of remapping, so
> > > I'll need to do some more reading. Thanks for the hints.
> > 
> > I forgot to ask. What's the advantage of having a contiguous virtual
> > memory area and splitting it up versus remapping each chunk separately?
> 
> Not alot, really, but it saves you from the pointer array and
> associated overhead. IIRC it is fairly easy to do in the kernel.
> 
> Arnd's version is good too, but you would be restricted to aligned
> powers of two for the bus number range in the DT, which is probably
> not that big a deal either?

I've been trying to make this work, but this implementation always
triggers a BUG_ON() in lib/ioremap.c, line 27:

        27              BUG_ON(!pte_none(*pte));

which seems to indicate that the page is already mapped, right?

Below is the relevant code:

struct tegra_pcie_bus {
        struct vm_struct *area;
        struct list_head list;
        unsigned int nr;
};

static struct tegra_pcie_bus *tegra_pcie_bus_alloc(struct tegra_pcie *pcie,
                                                   unsigned int busnr)
{
        unsigned long flags = VM_READ | VM_WRITE | VM_IO | VM_PFNMAP |
                              VM_DONTEXPAND | VM_DONTDUMP;
        phys_addr_t cs = pcie->cs->start;
        struct tegra_pcie_bus *bus;
        struct vm_struct *vm;
        unsigned int i;
        int err;

        bus = devm_kzalloc(pcie->dev, sizeof(*bus), GFP_KERNEL);
        if (!bus)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&bus->list);
        bus->nr = busnr;

        bus->area = get_vm_area(SZ_1M, VM_IOREMAP);
        if (!bus->area) {
                err = -ENOMEM;
                goto free;
        }

        for (i = 0; i < 16; i++) {
                unsigned long virt = (unsigned long)bus->area->addr +
                                     i * SZ_64K;
                phys_addr_t phys = cs + busnr * SZ_64K + i * SZ_1M;

                err = ioremap_page_range(virt, virt + SZ_64K - 1, phys,
                                         vm_get_page_prot(flags));
                if (err < 0) {
                        dev_err(pcie->dev, "ioremap_page_range() failed: %d\n",
                                err);
                        goto unmap;
                }
        }

        return bus;

unmap:
        vunmap(bus->area->addr);
        free_vm_area(bus->area);
free:
        devm_kfree(pcie->dev, bus);
        return ERR_PTR(err);
}

Anybody see what's wrong with that?

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