Andrew Sterian wrote:
On Mon, Jan 5, 2009 at 8:56 PM, Om <om.turyx@xxxxxxxxx> wrote:
Andrew Sterian wrote:
I'm developing a driver for an embedded ARM system (2.6.24 system) and
have 128M of RAM which I have been given free reign over. I want to
How do you define this free reign? Who is managing it ? kernel?
Whatever works...I am using mmap() to map the data from kernel to user
so I guess the kernel has to manage it.
If the kernel manages it, you don't have a free reign. Limiting kernel
memory access with mem= param would be a good idea.
I have the driver working with 8k of RAM, simply using kmalloc(). My
efforts to scale up to 8M have failed.
what I did was ioremap.
My case:
1. m/c had 256M
2. Passed parameter mem=128M to limit what cpu sees.
3. used ioremap on 0xc800_0000 (32bit processor) for 128M
4. used the returned virtual address.
OK, I tried this and it somewhat works (with MEM=120M in a 128M
system, 120M offset is 0xC7800000):
addr = ioremap(0xC7800000, 8*1024*1024);
printk(KERN_NOTICE "%08X\n", addr);
Strange is that the value of 'addr' when printed is 0xC7700000, or 1M
lower than I asked for.
It is indeed strange. After the call, what does
#cat /proc/iomem
say?
Now in my driver's mmap() function I write:
remap_pfn_range(vma, vma->vm_start,
__pa(addr) >> PAGE_SHIFT,
// ??? right ???
vma->vm_end - vma->vm_start,
vma->vm_page_prot);
The __pa() function returns 0x87700000 which I guess is right, except
for being 1M too low.
Is this the right way to do it?
Make sure that your PCI address space starts well above the physical address
present, so should the vmalloc_start address. I think you can change
#defines for these if required to suit your need.
If you have disabled pci (CONFIG_PCI = N et al), you don't have to worry
about pci address space.
No PCI in this system and I have no idea what vmalloc_start address is :)
In x86_64 and i386, you would find VMALLOC_{START,END} in pgtable.h
Thanks,
Om.
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