Messages in this thread | | | From | Andy Shevchenko <> | Date | Fri, 23 Feb 2018 19:12:44 +0200 | Subject | Re: [PATCH] scsi: lpfc: use memcpy_toio instead of writeq |
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On Fri, Feb 23, 2018 at 7:09 PM, David Laight <David.Laight@aculab.com> wrote: > From: Andy Shevchenko >> Sent: 23 February 2018 16:51 >> On Fri, Feb 23, 2018 at 6:41 PM, David Laight <David.Laight@aculab.com> wrote:
>> The side-effect I referred previously is about tails, i.e. unaligned >> bytes are transferred in portions >> like >> 7 on 64-bit will be 4 + 2 + 1, >> 5 = 4 + 1 > > on 64bit memcpy() is allowed to do: > (long *)(tgt+len)[-1] = (long *)(src+len)[-1]; > rep_movsq(tgt, src, len >> 3); > provided the length is at least 8. > > The misaligned PCIe transfer generates a single TLP covering 12 bytes with the > relevant byte enables set for the first and last 32bit words.
But is it guaranteed on any type of bus? memcpy_toio() is a generic helper, so, first of all we need to be sure what CPU on its side does, this is I think is pretty straight forward since it's all written in asm for 64-bit case. So, what about buses?
-- With Best Regards, Andy Shevchenko
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