hi
here is a piece of code from epson1356fb.c, inline
comments are what i understand, but i cant understand
somethings, kindly correct me where i am wrong and
thanks for your time in advance.
start = info->fix.membase_phys & PAGE_MASK;
>>> "start" now has the pfn of the fb's starting
physical address
len = PAGE_ALIGN((start & ~PAGE_MASK) +
info->fb_size);
>>> what does this line do ? , i think we get the
length of fb mem in "pages" .. like the total fb spans
2 pages, 3 pages etc .
off = vma->vm_pgoff << PAGE_SHIFT;
>>> what does vma->vm_pgoff really have, i assume it
has the "page offset" from the beginning of the file,
where this has to be mapped, like the "3rd page from
beginning of the file", so by left shifting it we get
the "relative" physical address from the start of the
file
if ((vma->vm_end - vma->vm_start + off) > len)
{
>>> "vma_end - vma_start" gives me the length of the
address to be mapped in bytes, which i add to off,
which currently is the relative address from the
beginnin of the file, but i dont do an & with
page_mask, hence i have some pfn+offset, this i
compare with a pure length in num of pages ???, am too
confused so let me not go any further ....
>>> one last question, what is the offset value i need
to pass to ioremap_page ...() function ?
DPRINTK("invalid vma\n");
return -EINVAL;
}
off += start;
vma->vm_pgoff = off >> PAGE_SHIFT;
pgprot_val(vma->vm_page_prot) &= ~_CACHE_MASK;
#ifdef SHADOW_FRAME_BUFFER
vma->vm_flags |= VM_RESERVED;
pgprot_val(vma->vm_page_prot) &=
~_CACHE_UNCACHED;
#else
pgprot_val(vma->vm_page_prot) |=
_CACHE_UNCACHED;
#endif
regards
Amit
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