On Sat, Aug 02, 2014 at 04:49:25PM +0200, Maxime Ripard wrote:

quoted

- 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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