[lkml]   [2012]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq
On Fri, Feb 3, 2012 at 00:05, H. Peter Anvin <> wrote:
> On 02/01/2012 05:05 PM, James Bottomley wrote:
>> Incidentally, the last time this came up was with mpt fusion: for a
>> write to a 64 bit register, it didn't care about order, but it did care
>> about interleaving as in if you write one half of a 64 bit register and
>> then write to another register, the 64 bit register effectively gets
>> written with zeros in the part you didn't write to, so we had to put a
>> spin lock in the open coded writeb/w/l/q() to make sure the card didn't
>> get interleaved writes.
> There are always going to be hardware which have specific needs, and for
> those open-coding makes sense, but the littleendian/bigendian pair is going
> to cover ~90% of users and make sense to can.
> I worked myself on a driver (which sadly never shipped) which had an WC
> window and a UC window... the final write in a series had a completion bit
> in it and would go to the UC window after setting up a whole chunk of
> operations in the WC window (writing UC memory flushes WC memory ahead of
> it.)
> Thus, the two-part breakdown of writeq() to the UC window had to write the
> low half to the WC window instead.  This is clearly not generic.
>        -hpa

Because of my ignorant, I don't know the words "UC window" and "WC window"
in this context. Could you teach me?

Hitoshi Mitake
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2012-02-04 16:41    [from the cache]
©2003-2014 Jasper Spaans. hosted at Digital Ocean