Hi, Rob, On 3/4/24 16:56, Rob Herring wrote: > On Sat, Mar 02, 2024 at 10:23:16AM -0600, Sam Protsenko wrote: >> On Sat, Mar 2, 2024 at 3:36 AM Tudor Ambarus <tudor.ambarus@xxxxxxxxxx> wrote: >>> >>> >>> >>> On 01.03.2024 22:42, Mark Brown wrote: >>>> On Fri, Mar 01, 2024 at 01:28:35PM -0600, Sam Protsenko wrote: >>>>> On Fri, Mar 1, 2024 at 5:55 AM Tudor Ambarus <tudor.ambarus@xxxxxxxxxx> wrote: >>>> >>>>>> Since the addition of the driver in 2009, the driver selects between DMA >>>>>> and polling mode depending on the transfer length - DMA mode for >>>>>> transfers bigger than the FIFO depth, polling mode otherwise. All >>>>>> versions of the IP support polling mode, make the dma properties not >>>>>> required. >>>> >>>>> AFAIU, the device tree has nothing to do with drivers, it's about >>>>> hardware description. Does making DMA properties not required here >>> >>> correct >>> >>>>> mean that there are some HW out there which doesn't integrate DMA in >>> >>> no, to me it means that the IP can work without DMA, only in PIO mode, >>> regardless if DMA is integrated or not. Not required means that the >>> property is not mandatory, which is what I'm trying to achieve here. >>> >>>>> SPI blocks? Even if this change is ok (I'm not sure), the >>>>> argumentation doesn't look sound to me. >>> >>> switching to PIO mode in the driver for sizes smaller than FIFO depths >>> in the driver guarantees that all existing compatibles support PIO mode. >>> >>> Are you saying that if there is a physical line between an IP and DMA >>> controller, then the DMA properties must always be specified in dt? I >>> thought they can be marked as optional in this case, and that's what I >>> did with this patch. >>> >> >> No, I would wait for maintainers to clarify on that bit. Change itself >> can be ok. But the commit message shouldn't mention the driver, >> because the driver uses (depends on) device tree, not vice versa. The >> device tree can be used in other projects as well (like U-Boot and >> OP-TEE), so it should be designed to be universal and not depend on >> kernel drivers. The commit message should be based on particular HW >> layout features and how the patch makes the bindings describe that HW >> better. It shouldn't rely on driver implementations. > > If the controller is DMA capable then it should have dma properties. The should have as in required/mandatory? > compatible should be enough to tell if it is a case of 'can only work yes, I agree > with DMA'. Otherwise, it is going to be up to a specific user. Even > within Linux, you may have a serial port that doesn't use DMA for the > console, but uses it for the tty or serdev. > > Of course, if a new device is added without DMA properties and they > are added later on, then they are going to be optional even though the > DMA support is always there. I can't fully understand everyone's h/w. > The SPI controller that I'm working with has a dedicated channel to the DMA controller. It can work without DMA too, just by polling registers or by interrupts. I can't get the DMA controller to work correctly yet, and since the SPI controller can work without DMA, I thought that I can mark the DMA properties as optional, add the SPI node in dt without DMA, and add the DMA properties later on, after I have the DMA controller working correctly. Is this approach wrong? Thanks, ta
