On 13/09/2019 17.36, Rob Herring wrote: > On Tue, Sep 10, 2019 at 02:50:35PM +0300, Peter Ujfalusi wrote: >> On systems where multiple DMA controllers available, non Slave (for example >> memcpy operation) users can not be described in DT as there is no device >> involved from the DMA controller's point of view, DMA binding is not usable. >> However in these systems still a peripheral might need to be serviced by or >> it is better to serviced by specific DMA controller. >> When a memcpy is used to/from a memory mapped region for example a DMA in the >> same domain can perform better. >> For generic software modules doing mem 2 mem operations it also matter that >> they will get a channel from a controller which is faster in DDR to DDR mode >> rather then from the first controller happen to be loaded. >> >> This property is inherited, so it may be specified in a device node or in any >> of its parent nodes. > > If a device needs mem2mem dma, I think we should just use the existing > dma binding. The provider will need a way to define cell values which > mean mem2mem. But isn't it going to be an abuse of the binding? Each DMA controller would hack this in different ways, probably using out of range DMA request/trigger number or if they have direction in the binding or some other parameter would be set to something invalid... > For generic s/w, it should be able to query the dma speed or get a > preferred one IMO. It's not a DT problem. > > We measure memcpy speeds at boot time to select the fastest > implementation for a chip, why not do that for mem2mem DMA? It would make an impact on boot time since the tests would need to be done with a large enough copy to be able to see clearly which one is faster. Also we should be able to handle different probing orders: client1 should have mem2mem channel from dma2. - dma1 probes - client1 probes and asks for a mem2mem channel - dma2 probes Here client1 should deffer until dma2 is probed. Probably the property should be dma-mem2mem-domain to be more precise on it's purpose and avoid confusion? > >> >> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx> >> --- >> .../devicetree/bindings/dma/dma-domain.yaml | 88 +++++++++++++++++++ >> 1 file changed, 88 insertions(+) >> create mode 100644 Documentation/devicetree/bindings/dma/dma-domain.yaml > > Note that you have several errors in your schema. Run 'make dt_bindings_check'. That does not do anything on my system, but git dt-doc-validate running via https://github.com/robherring/yaml-bindings.git. - Péter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
