Messages in this thread | | | Date | Wed, 12 Sep 2012 18:54:27 -0400 | From | Cyril Chemparathy <> | Subject | Re: [PATCH v2] /dev/mem: use phys_addr_t for physical addresses |
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Greg,
On 9/12/2012 2:15 PM, Greg KH wrote: > On Wed, Sep 12, 2012 at 02:05:58PM -0400, Cyril Chemparathy wrote: >> This patch fixes the /dev/mem driver to use phys_addr_t for physical >> addresses. This is required on PAE systems, especially those that run >> entirely out of >4G physical memory space. > > What is the symptom if this patch is not applied? Does it need to be > backported to older kernels? If so, which ones? >
As far as I can tell, this change only benefits platforms where lowmem lies outside the 32-bit addressable range. On the ARM based KeyStone platform, all of our memory is located above the 4GB limit at 0x8:0000:0000. On this platform, trying to read lowmem breaks as follows:
# dd if==/dev/mem of=/dev/null bs==4k count=1 skip=8388608 dd: /dev/mem: Bad address
Assuming that we are unique in this regard (i.e. lowmem outside 4GB), I don't see any reason to backport this to earlier kernels.
-- Thanks - Cyril
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