On Sat, Aug 02, 2014 at 04:49:25PM +0200, Maxime Ripard wrote: > > - 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? - residue is for the descriptor asked - not for the current active one - we can store the size locally and return that when not processing - arg txstate can be null > 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 ? Ah no. The model doesn't assume the config will be written runtime. So the descriptor which are already prepared doesn't change with DMA_SLAVE_CONFIG call. Only new descriptors will take those values But yes the pause/resume would be syncronous HTH -- ~Vinod
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