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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 12:00 +0100
Message-ID <sM4AF-57U-21@gated-at.bofh.it> (permalink)
References (5 earlier) <sLnm3-26m-69@gated-at.bofh.it> <sLnP3-2vS-17@gated-at.bofh.it> <sLNq9-2vj-35@gated-at.bofh.it> <sLNzQ-2yE-21@gated-at.bofh.it> <sM4hj-51v-15@gated-at.bofh.it>
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On 08/12/2016 11:39, Vinod Koul wrote:

> On Wed, Dec 07, 2016 at 04:45:58PM +0000, Måns Rullgård wrote:
>
>> Vinod Koul <vinod.koul@intel.com> writes:
>>
>>> On Tue, Dec 06, 2016 at 01:14:20PM +0000, Måns Rullgård wrote:
>>>>
>>>> That's not going to work very well.  Device drivers typically request
>>>> dma channels in their probe functions or when the device is opened.
>>>> This means that reserving one of the few channels there will inevitably
>>>> make some other device fail to operate.
>>>
>>> No that doesn't make sense at all, you should get a channel only when you
>>> want to use it and not in probe!
>>
>> Tell that to just about every single driver ever written.
> 
> Not really, few do yes which is wrong but not _all_ do that.

Vinod,

Could you explain something to me in layman's terms?

I have a NAND Flash Controller driver that depends on the
DMA driver under discussion.

Suppose I move the dma_request_chan() call from the driver's
probe function, to the actual DMA transfer function.

I would want dma_request_chan() to put the calling thread
to sleep until a channel becomes available (possibly with
a timeout value).

But Maxime told me dma_request_chan() will just return
-EBUSY if no channels are available.

Am I supposed to busy wait in my driver's DMA function
until a channel becomes available?

I don't understand how the multiplexing of few memory
channels to many clients is supposed to happen efficiently?

Regards.

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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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