On Fri, Aug 07, 2015 at 12:07:11PM -0400, Peter Hurley wrote:
> On 08/07/2015 11:29 AM, Russell King - ARM Linux wrote:
> > On Fri, Aug 07, 2015 at 11:08:48AM -0400, Peter Hurley wrote:
> >> [ + Greg KH ]
> >>
> >> On 08/07/2015 09:57 AM, Russell King - ARM Linux wrote:
> >>> As it is something that the driver has _not_ supported, you are clearly
> >>> adding a feature to an existing driver. It's not a bug fix.
> >>>
> >>>>> If something else has been converted to pause channels and that is
> >>>>> causing
> >>>>> a problem, then _that_ conversion is where the bug lies, not the lack of
> >>>>> support in the omap-dma.
> >>
> >> FWIW, the actual bug is the api that silently does nothing.
> >
> > Incorrect.
> >
> > static int omap_dma_pause(struct dma_chan *chan)
> > {
> > struct omap_chan *c = to_omap_dma_chan(chan);
> >
> > /* Pause/Resume only allowed with cyclic mode */
> > if (!c->cyclic)
> > return -EINVAL;
> >
> > Asking for the channel to be paused will return an error code indicating
> > that the request failed. That will be propagated back through to the
> > return code of dmaengine_pause().
> >
> > If we look at what 8250-dma.c is doing:
> >
> > if (dma->rx_running) {
> > dmaengine_pause(dma->rxchan);
> >
> > It's 8250-dma.c which is silently _ignoring_ the return code, failing
> > to check that the operation it requested worked. Maybe this should be
> > WARN_ON(dmaengine_pause(dma->rxchan)) or at least it should print a
> > message?
>
> Thanks for the suggestion; I'll hold on to that and push it after we add
> the 8250 omap dma pause in mainline.
Why wait? You're hiding a data loss bug which is clearly the result of
code you allegedly maintain.
> Well, instead of me saying something snide about the lack of upstream serial
> driver unit tests, I'll say I've been working on cleaning up and organizing
> my own tty/serial subsystem and driver units tests which I hope to upstream
> in the fall.
>
> Those include i/o validators that ran this driver for days at time without
> error at max line rate. Unfortunately, that hardware does not exhibit the
> same problem as the DRA7 noted in the changelog.
What you have is a race condition in the code you a responsible for
maintaining, caused by poorly implemented code. Fix it, rather than
whinging about drivers outside of your subsystem having never implemented
_optional_ things that you choose to merge broken code which relied upon
it _without_ checking that the operation succeeded.
It is _entirely_ your code which is wrong here.
I will wait for that to be fixed before acking the omap-dma change since
you obviously need something to test with.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
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