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Paulo Zanoni authored
On IVB and older, we basically have two registers: the control and the data register. We write a few consecutitve times to the control register, and we need these writes to arrive exactly in the specified order. Also, when we're changing the data register, we need to guarantee that anything written to the control register already arrived (since changing the control register can change where the data register points to). Also, we need to make sure all the writes to the data register happen exactly in the specified order, and we also *can't* read the data register during this process, since reading and/or writing it will change the place it points to. So invoke the "better safe than sorry" rule and just be careful and put barriers everywhere :) On HSW we still have a control register that we write many times, but we have many data registers. Demanded-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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