howto use ioremap_wc?
From: Brice Goglin
Date: Sat May 31 2008 - 05:03:21 EST
Hello,
We're looking at using ioremap_wc() in myri10ge. No drivers seem to be
using it yet, so I'd like to get some clarification regarding ioremap_wc
failures, MTRR and so on.
What we currently do is mtrr_add() and then ioremap. Depending on the
mtrr_add() success, we use the "wc_fifo" or regular PIO with fences to
submit requests to the NIC. How are we supposed to switch this to
ioremap_wc?
Are we sure that if the arch supports _wc, it does not return success
when the underlying plain ioremap worked but setting up _wc() failed? If
so, why does it revert to ioremap_nocache when PAT isn't enabled?
Can we keep the mtrr_add() in the regular path? Or are we supposed to
drop it when the arch provides ioremap_wc and it did not fail?
thanks,
Brice
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