On 11/02/2025 09:23, Paul-pl Chen (陳柏霖) wrote: > On Sat, 2025-01-18 at 09:37 +0100, Krzysztof Kozlowski wrote: >> >>> >>> (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 >> >> >> > > Hi KK, > > Sorry, I just found this email was not send. > > This email is discuss about the EXDMA under the display subsystem > > The current placement of EXDMA under the display subsystem in > Mediatek's architecture is primarily due to its functional role as a > sub-device within the display pipeline. > > In MT8196 hardware design, the sub-devices in display pipeline follow a > sequence of: EXDMA -> BLENDER -> OUTPROC -> PQ -> DVO. > > In MT8195 hardware design, the sub-devices in display pipeline follow a > sequence of: OVL -> PQ ->DSI. > > As we see, OVL has been divided into three new hardware IPs in MT8196. > OVL and EXDMA both have the ability to fetch data directly from DRAM > and can be regarded as DMA controller. > > I also have confirmed with the hardware designer that EXDMA is a kind > of DMA, but it is specially designed to handle the graphical layer, and > has better performance than ordinary DMA. To me the decisive factor is that you use dma-cells here, so it is a DMA controller. DMA controllers should placed in a directory of their maintainer, so they can review it. > > Therefore, I think that moving EXDMA and OVL from the display folder to > the DMA folder, or only kepping them in the display folder is decided > by the two different views of DMA ability or display sub-device. > > We will follow your instructions to put EXDMA on the place you decided. > > > Best, Paul > Best regards, Krzysztof
