On Fri, Aug 01, 2014 at 10:43:06PM +0530, Vinod Koul wrote: > On Thu, Jul 31, 2014 at 06:23:30PM +0200, Maxime Ripard wrote: > > On Thu, Jul 31, 2014 at 05:26:28PM +0530, Vinod Koul wrote: > > > > Also, feel free to add anything that you feel like you keep saying > > during the review. If mistakes keep coming, it's probably worth > > documenting what you expect. > I think the common issues seen would be: > - prpeare calls in atomic context and usuage of GFP_NOWAIT for memory > allocations I think we have that part covered already. > - residue callculation, though situation is much better now but still lots > of driver do it worng and folks do get it wrong What mistake in often made regarding the residue calculation? > > > > Because, for the moment, we're pretty much left in the dark with > > > > different drivers doing the same thing in completetely different ways, > > > > with basically no way to tell if it's either the framework that > > > > requires such behaviour, or if the author was just feeling creative. > > > > > > > > There's numerous examples for this at the moment: > > > > - The GFP flags, with different drivers using either GFP_ATOMIC, > > > > GFP_NOWAIT or GFP_KERNEL in the same functions > > > > - Having to set device_slave_caps or not? > > > > - Some drivers use dma_run_depedencies, some other don't > > > > - That might just be my experience, but judging from previous > > > > commits, DMA_PRIVATE is completely obscure, and we just set it > > > > because it was making it work, without knowing what it was > > > > supposed to do. > > > > - etc. > > > > > > Thanks for highlighting we should definitely add these in Documentation > > > > It's quite clear in the case of the GFP flags now, Lars-Peter and you > > cleared up device_slave_caps, but I still could use some help with > > DMA_PRIVATE. > > > > > > And basically, we have no way to tell at the moment which one is > > > > right and which one needs fixing. > > > > > > > > The corollary being that it cripples the whole community ability to > > > > maintain the framework and make it evolve. > > > > > > > > > > + * device_slave_caps > > > > > > + - Isn't that redundant with the cap_mask already? > > > > > > + - Only a few drivers seem to implement it > > > > > For audio to know what your channel can do rather than hardcoding it > > > > > > > > Ah, yes, I see it now. It's not related to the caps mask at all. > > > > > > > > Just out of curiosity, wouldn't it be better to move this to the > > > > framework, and have these informations provided through the struct > > > > dma_device? Or would it have some non-trivial side-effects? > > > Well the problem is ability to have this queried uniformly from all drivers > > > across subsystems. If we can do this that would be nice. > > > > I can work on some premelinary work to do just that, and see if it > > works for you then. > Sure sounds excellent to me Another extra questions arose during starting this. In the case of the call to device_control, especially in the DMA_SLAVE_CONFIG case, but that also applies to pause/resume, are the changes supposed to be immediates or can they happen later? I actually have in mind the case where we would use a vchan, that might or might not be actually mapped to a physical channel at the moment where the DMA_SLAVE_CONFIG call is made. In the case where it's not mapped and not transfering anything, it's pretty trivial, to handle, but in the case where it's actually mapped to a physical channel, should we push the new configuration to the physical channel right away, or can it wait until the transfer ends ? Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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