12:55 <dramforever[m]1> i'm gonna pretend this is a riscv question because it pertains to the spacemit k1. they made the incredible decision to split up RAM into a below 2G part and an above 4G part, and also somewhat patches up the hole by mapping DMA accesses, e.g. first 2G of RAM above 4G is DMA accessible starting at 0x8000_0000 for ethernet and a few others

12:55 <dramforever[m]1> now do do this obviously we're gonna need a few more bus nodes with dma-ranges. question is: what do we call those nodes?

12:56 <dramforever[m]1> they can't all be bus, or bus@0, or bus@80000000...

12:56 <dramforever[m]1> (bus nodes in devicetree, i mean, accidentally edited that part out)

12:56 <bjdooks> some systems w/o iommu had 32bit only dma peripherals or thought that might be the case

12:57 <dramforever[m]1> that part is normal and in fact works

12:58 <dramforever[m]1> the funny here is spacemit designed their SoC with static "IOMMU" maps

12:59 <dramforever[m]1> so for example, the simplest of these is range 5, which has dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>, <0x0 0x80000000 0x1 0x00000000 0x0 0x80000000>;

12:59 <dramforever[m]1> https://github.com/spacemit-com/linux-k1x/blob/k1/arch/riscv/boot/dts/spacemit/k1-x.dtsi

12:59 <bjdooks> the absolute pain when people made socs w/o any mem in 32bit mem space and no iumu

12:59 <bjdooks> at least you can work around it in dt

12:59 <dramforever[m]1> i don't know if i'm supposed to tell you, but yeah those are incredibly frustrating

12:59 <bjdooks> i had one soc where to make the dram and core coherent with periphjerals they just bridged the incoing dma into the core coplex with a static map

12:59 <dramforever[m]1> *tell you what i've seen

13:00 <dramforever[m]1> well, that's sifive's favorite right?

13:01 <dramforever[m]1> also i do not need to be coherent with your core

13:04 <dramforever[m]1> yeah whatever i should probably just ask rob herring...

14:02 <palmer> dramforever[m]1: there's a DT channel, Rob and Conor are usually in there

14:05 <dramforever[m]1> til, thanks palmer

14:07 <palmer> NP. Aside from just generally RISC-V people having to deal with stupid hardware and maybe tripping over this sort of thing, you’re probably better off over there — that’s where the people who actually understand DT hang out

14:07 <dramforever[m]1> TIL there's irc in MAINTAINERS

14:08 <palmer> Ya, there’s a bunch in there

14:08 <dramforever[m]1> it's a treasure trove in there, i thought it's just a giant db for get_maintainers.pl

14:08 <palmer> Nope, all sorts of fun stuff ;)