Re: [PATCH] dmaengine: device must have at least one channel

[Greg Kroah-Hartman]

On Mon, Aug 08, 2016 at 08:24:49AM -0700, Viresh Kumar wrote:
> On 08-08-16, 13:47, Vinod Koul wrote:
> > On Fri, Aug 05, 2016 at 09:30:50AM -0700, Viresh Kumar wrote:
> > > On 03-08-16, 21:34, Greg Kroah-Hartman wrote:
> > 
> > > > To follow up on this, as you found out, this patch breaks working
> > > > hardware, so please don't apply it anywhere.  It needs more debugging to
> > > > figure out exactly what is going on with some very strange hardware that
> > > > seems to be relying on some strange code...
> > > 
> > > Thanks for your email Greg, and I know what the issue is.
> > > 
> > > So, the dmaengine core actually allows registering a device without any channels
> > > and the dma driver can add channels later (directly to the dma-device channel
> > > list), for example, from the of-xlate callback once someone requests for a
> > > channel.
> > 
> > I do not think that is good idea
> > 
> > > Though its not the right way of doing things, but it still works. The only thing
> > > which breaks in that case is sysfs interface to dmaengine as the channels aren't
> > > registered as devices and so they aren't visible in userspace, as that code is
> > > *only* executed while the dma-device is registered.
> > > 
> > > I think its dmaengine core's decision to keep supporting such drivers or not and
> > > so I would like Vinod to comment on that..
> > 
> > My view would be to ensure that controllers have channels before they
> > register. If they dont, then please register later.
> > 
> > > But if we do want to support such drivers, then the core must be updated to fix
> > > the memleak I reported here, as idr_ref is allocated and not used at all (also
> > > dma-id allocated for it).
> > > 
> > > Or provide another API to properly and fully add channels at a later point of
> > > time.
> > 
> > And looking at drivers, I am not seeing anyone who needs such a support, so
> > am not inclined to support such a feature atm.
> 
> Right and so I believe that applying this patch is the right thing to do..

So only the drivers that are out-of-tree are broken with this patch?

I like it :)

greg k-h