Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1530325

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 2016-11-25 16:10 +0100
Message-ID <sHqiu-2aY-43@gated-at.bofh.it> (permalink)
References (4 earlier) <sHoTo-18u-15@gated-at.bofh.it> <sHpcK-1fd-27@gated-at.bofh.it> <sHpcK-1fd-25@gated-at.bofh.it> <sHpmq-1yD-25@gated-at.bofh.it> <sHpFL-1In-17@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

On 25/11/2016 15:17, Russell King - ARM Linux wrote:
> On Fri, Nov 25, 2016 at 02:03:20PM +0000, Måns Rullgård wrote:
>> Russell King - ARM Linux <linux@armlinux.org.uk> writes:
>>
>>> On Fri, Nov 25, 2016 at 01:50:35PM +0000, Måns Rullgård wrote:
>>>> Russell King - ARM Linux <linux@armlinux.org.uk> writes:
>>>>> It would be unfair to augment the API and add the burden on everyone
>>>>> for the new API when 99.999% of the world doesn't require it.
>>>>
>>>> I don't think making this particular dma driver wait for the descriptor
>>>> callback to return before reusing a channel quite amounts to a horrid
>>>> hack.  It certainly wouldn't burden anyone other than the poor drivers
>>>> for devices connected to it, all of which are specific to Sigma AFAIK.
>>>
>>> Except when you stop to think that delaying in a tasklet is exactly
>>> the same as randomly delaying in an interrupt handler - the tasklet
>>> runs on the return path back to the parent context of an interrupt
>>> handler.  Even if you sleep in the tasklet, you're sleeping on behalf
>>> of the currently executing thread - if it's a RT thread, you effectively
>>> destroy the RT-ness of the thread.  Let's hope no one cares about RT
>>> performance on that hardware...
>>
>> That's why I suggested to do this only if the needed delay is known to
>> be no more than a few bus cycles.  The completion callback is currently
>> the only post-transfer interaction we have between the dma and device
>> drivers.  To handle an arbitrarily long delay, some new interface will
>> be required.
> 
> And now we're back at the point I made a few emails ago about undue
> burden which is just about quoted above...

I've had several talks with the HW dev, and I don't think they
anticipated the need to mux the 3 channels. In their minds,
customers would choose at most 3 devices to support, and
assign one channel to each device statically.

In fact, in tango4, supported devices are:
A) NAND Flash controllers 0 and 1
NB: the upstream driver only uses controller 0
B) IDE or SATA controllers 0 and 1
C) a few crypto HW blocks which do not work as expected (unused)

Customers typically use 1 channel for NAND, maybe 1 for SATA,
and 1 channel remains unused.

I understand the desire to solve the general case in the
driver, but actual use-cases are much more trivial.

Regards.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-23 11:30 +0100
  Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-23 13:20 +0100
    Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-23 13:50 +0100
      Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-23 18:30 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-24 12:00 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-24 15:20 +0100
            Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-24 16:30 +0100
              Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-24 17:40 +0100
  Re: Tearing down DMA transfer setup after DMA client has finished Vinod Koul <vinod.koul@intel.com> - 2016-11-25 05:50 +0100
    Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 13:00 +0100
      Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 15:10 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 15:20 +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 15:50 +0100
    Re: Tearing down DMA transfer setup after DMA client has finished Russell King - ARM Linux <linux@armlinux.org.uk> - 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 14:10 +0100
        Re: Tearing down DMA transfer setup after DMA client has finished Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-11-25 14:40 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-11-25 15:00 +0100
            Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 15:10 +0100
              Re: Tearing down DMA transfer setup after DMA client has finished Russell King - ARM Linux <linux@armlinux.org.uk> - 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 15:50 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-11-25 16:00 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 16:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 16:10 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 16:20 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 16:30 +0100
                Re: Tearing down DMA transfer setup after DMA client has finished Mason <slash.tmp@free.fr> - 2016-11-25 16:30 +0100
          Re: Tearing down DMA transfer setup after DMA client has finished Måns Rullgård <mans@mansr.com> - 2016-11-25 15:00 +0100
    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

csiph-web