Re: Tearing down DMA transfer setup after DMA client has finished

From	Mason <slash.tmp@free.fr>
Newsgroups	linux.kernel
Subject	Re: Tearing down DMA transfer setup after DMA client has finished
Date	2016-12-08 13:50 +0100
Message-ID	<sM6j8-6ce-9@gated-at.bofh.it> (permalink)
References	(8 earlier) <sLNzQ-2yE-21@gated-at.bofh.it> <sM4hj-51v-15@gated-at.bofh.it> <sM5n3-5Di-3@gated-at.bofh.it> <sM5Gq-5YO-27@gated-at.bofh.it> <sM5ZM-65C-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 08/12/2016 13:20, Måns Rullgård wrote:

> The only problem we have is that nobody envisioned hardware where the
> dma engine indicates completion slightly too soon.  I suspect there's a
> fifo or such somewhere, and the interrupt is triggered when the last
> byte has been placed in the fifo rather than when it has been removed
> which would have been more correct.

As I (tried to) explain here:
https://marc.info/?l=dmaengine&m=148007808418242&w=2

A *read* MBUS agent raises its IRQ when it is safe for the memory
to be overwritten (i.e. every byte has been pushed into the pipe).

A *write* MBUS agent raises its IRQ when it is safe for another
agent to read any one of the transferred bytes.

The issue comes from the fact that, for a memory-to-device transfer,
the system will receive the read agent's IRQ, but most devices
(NFC, SATA) don't have an IRQ line to signal that their part of the
operation is complete.

As I explained, if one sets up a memory-to-memory DMA copy, then
the system will actually receive *two* IRQs.

Regards.

Thread

Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 13:50 +0100
  Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 14:20 +0100
    Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 15:30 +0100
      Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 15:40 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 16:50 +0100
  Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-29 19:30 +0100
    Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-06 06:10 +0100
      Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-06 13:50 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-06 14:20 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-06 16:30 +0100
            Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-06 16:40 +0100
              Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-07 00:00 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-07 17:40 +0100
            Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-07 17:50 +0100
              Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 11:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-08 12:00 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-08 12:20 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 12:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-08 13:10 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-08 13:20 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 13:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 17:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 17:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-09 08:10 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Sebastian Frias <sf84@laposte.net> - 2016-12-09 11:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-09 12:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished 1Måns Rullgård <mans@mansr.com> - 2016-12-09 12:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-09 18:20 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-09 18:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-09 19:00 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-09 18:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-09 19:00 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-09 19:20 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-09 19:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 12:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-08 13:10 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 13:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Geert Uytterhoeven <geert@linux-m68k.org> - 2016-12-08 13:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 13:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-08 14:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 14:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-08 13:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 16:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 17:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 16:40 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-12-08 16:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 17:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 17:50 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-07 17:40 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-07 17:50 +0100
            Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-12-08 11:30 +0100
              Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-12-08 12:50 +0100

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