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omap-dma + 8250_omap: fix the dmaengine_pause()

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  omap-dma + 8250_omap: fix the dmaengine_pause() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-07 22:10 +0200
    [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause is not supported Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-07 22:10 +0200
      Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Peter Hurley <peter@hurleysoftware.com> - 2015-08-08 02:30 +0200
        Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-08 11:10 +0200
          Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Vinod Koul <vinod.koul@intel.com> - 2015-08-11 12:00 +0200
        Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-08 11:40 +0200
          Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-08 12:00 +0200
          Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Greg KH <greg@kroah.com> - 2015-08-08 17:50 +0200
      Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause is  not supported Peter Ujfalusi <peter.ujfalusi@ti.com> - 2015-08-10 14:00 +0200
        Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-10 14:20 +0200
        Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Peter Hurley <peter@hurleysoftware.com> - 2015-08-10 15:10 +0200
          Re: [PATCH 1/3] tty: serial: 8250_omap: do not use RX DMA if pause  is not supported Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-10 19:20 +0200
    [PATCH v3 3/3] dma: omap-dma: add support for pause of non-cyclic transfers Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-07 22:10 +0200
      Re: [PATCH v3 3/3] dma: omap-dma: add support for pause of non-cyclic  transfers Peter Ujfalusi <peter.ujfalusi@ti.com> - 2015-08-11 14:10 +0200
        Re: [PATCH v3 3/3] dma: omap-dma: add support for pause of  non-cyclic transfers Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-11 14:40 +0200
          Re: [PATCH v3 3/3] dma: omap-dma: add support for pause of non-cyclic  transfers Peter Ujfalusi <peter.ujfalusi@ti.com> - 2015-08-11 14:50 +0200
    [PATCH 2/3] dma: add __must_check annotation for dmaengine_pause() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-07 22:10 +0200
      Re: [PATCH 2/3] dma: add __must_check annotation for dmaengine_pause() Peter Hurley <peter@hurleysoftware.com> - 2015-08-08 02:50 +0200
      Re: [PATCH 2/3] dma: add __must_check annotation for  dmaengine_pause() Vinod Koul <vinod.koul@intel.com> - 2015-08-11 12:00 +0200
        Re: [PATCH 2/3] dma: add __must_check annotation for  dmaengine_pause() Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-11 12:10 +0200
          Re: [PATCH 2/3] dma: add __must_check annotation for dmaengine_pause() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2015-08-11 14:40 +0200

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#1205104 — Re: [PATCH 2/3] dma: add __must_check annotation for dmaengine_pause()

On 08/11/2015 12:06 PM, Russell King - ARM Linux wrote:
> I think what people need to learn is that an API in the kernel which
> returns an int _can_ fail - it returns an int so it _can_ return an
> error code.  If it _can_ return an error code, there _will_ be
> implementations which _do_.
> 
> If you don't check the return code, either your code doesn't care whether
> the function was successful or not, or you're playing with fire.  This is
> a prime example of playing with fire.
> 
> Let's leave the crappy userspace laziness with regard to error checking
> to userspace, and keep it out of the kernel.
> 
> Yes, the DMA engine capabilities may not be sufficient to describe every
> detail of DMA engines, but that's absolutely no reason to skimp on error
> checking.  Had there been some kind of error checking at the site, this
> problem would have been spotted before the 8250-omap driver was merged.

Let me disable RX-DMA in 8250-omap code and push that stable. Then we
won't need a special annotation for pause support because it remains
off and is currently about one user. I browsed each driver in
drivers/dma each one which does support pause supports it and all of
them implement it unconditionally (ipu_idmac grabs a mutex first but
this is another story).
Adding error checking to 8250-omap like I have it in #1 and disabling
RX-DMA in case pause fails looks be reasonable since there is nothing
else that can be done I guess.
Once we have the missing piece in omap-dma the RX-DMA can be enabled in
8250-omap.
Does this sound like a plan we can agree on?

Sebastian
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