On 17/01/2025 11:36, Paul-pl Chen (陳柏霖) wrote: >>> b/Documentation/devicetree/bindings/display/mediatek/mediatek,exdma >>> .yaml >> >> Filename matching compatible. >> >> Why is this in display? DMA goes to dma. > > Hi Krzysztof , > > Regarding the issue of the EXDMA driver, we have conducted an internal > survey of drivers under the DMA subsystem. We found that EXDMA operates I did not talk about driver. I talked about this patch. Look at patch title - it starts with dt-bindings. Is here anything about driver? No. Why do we talk about driver? > differently from typical DMA drivers, and therefore we believe that the > EXDMA driver may not be suitable to be placed under the > driver/mediatek/drm directory. The main reasons are as follows: > > (1)No Memory Allocation within EXDMA Engine: > The EXDMA engine does not perform memory allocation operations itself. > Instead, it relies on GEM (Graphics Execution Manager) to allocate > memory.Traditional DMA drivers often handle their own memory > allocations, but in the case of EXDMA, memory management is delegated > to GEM. > > (2)Primary Task of EXDMA: > The main function of EXDMA is to transfer buffers allocated by GEM to > the subsequent display pipeline. > EXDMA serves as a bridge between memory allocated by GEM and the > display components, rather than acting as a general-purpose DMA engine. > Based on the points above, we have decided to place the EXDMA driver > under the DRM display subsystem rather than under the DMA subsystem. I don't care if it uses GEM or kernel allocator or even 3rd party allocator. The question is: what is this device? If it is performing DMA, then it should be placed in "dma" directory. The rdma was placed differently but as you can easily check: it was never acked/reviewed, so don't use it as an example. Of course if it does not perform DMA, then it should not be in dma, but then I don't agree on using dma-cells here and anything like that in the driver. Best regards, Krzysztof
