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

From: Sebastian Andrzej Siewior
Date: Tue Aug 11 2015 - 08:34:37 EST

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
Does this sound like a plan we can agree on?

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