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