On 08/07/2015 12:39 PM, Russell King - ARM Linux wrote:
> On Fri, Aug 07, 2015 at 05:44:03PM +0200, Sebastian Andrzej Siewior wrote:
>> On 08/07/2015 05:29 PM, 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?
>>
>> I think this is what Peter meant by saying "silently does nothing".
>
> Maybe Peter should phrase his replies better. "the actual bug is the
> api that silently does nothing." to me means he is complaining that
> dmaengine_pause() had no effect. _That_ is what I'm objecting to,
> and claiming that Peter's comment is wrong.
Yes, I missed that the api included a return code which the 8250 dma
code should be checking.
> He's now blaming me for snide remarks. I could call his one above an
> incorrect snide remark against the quality of DMA engine code.
You'd be reading a lot into my statement.
> He's
> totally wrong, and been proven wrong by my analysis above, plain and
> simple.
>
> He should now accept that he's wrong
Done.
> and move along with sorting out
> this mess _without_ requiring optional features to be implemented in
> other subsystems to fix bugs in code he's supposed to be maintaining.
This is simply a bug that flew under the radar, much like every other
bug that gets fixed daily in mainline.
The omap-serial driver which doesn't use dma is still the preferred
stable driver for omap, for the moment.
One of the main features of the 8250_omap integration was the addition
of dma support. Without it, 8250_omap is ttyO in ttyS clothing.
Regards,
Peter Hurley
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