On Thu, Apr 23, 2020 at 05:45:55PM +0200, H. Nikolaus Schaller wrote: > > Am 23.04.2020 um 17:00 schrieb Neil Armstrong <narmstrong@xxxxxxxxxxxx>: > >> One thing we can learn is that "core" seems to be a de facto standard > >> for the core clock-name. An alternative "gpu" is used by nvidia,gk20a.txt. > > > > Usually IPs needs a few clocks: > > - pclk or apb or reg: the clock clocking the "slave" bus to serve the registers > > - axi or bus or ahb: the bus clocking the the "master" bus to get data from system memory > > - core: the actual clock feeding the GPU logic > > And the sgx544 seems to have two such clocks. > > > Sometimes you have a single clock for slave and master bus. > > > > But you can also have separate clocks for shader cores, .. this depends on the IP and it's architecture. > > The IP can also have memories with separate clocks, etc... > > Indeed. > > > But all these clocks can be source by an unique clock on a SoC, but different on another > > SoC, this is why it's important to list them all, even optional. > > > > You'll certainly have at least a reset signal, and a power domain, these should exist and be optional. > > Well, they exist only as hints in block diagrams of some SoC data > sheets (so we do not know if they represent the imagination > definitions) and the current driver code doesn't make use of it. Still > the gpu core works. > > So I do not see any urgent need to add a complete list to the bindings > now. > > Unless some special SoC integration makes use of them. Then it is IMHO > easier to extend the bindings by a follow-up patch than now thinking > about all potential options and bloating the bindings with things we > (the open source community) doesn't and can't know. > > My goal is to keep the bindings as minimalistic as possible. And reset > lines and power domains are (at least for those we have in the works) > not needed to make working systems. > > Therefore, for clocks I also would start with a minimalistic approach > for a single optional GPU core clock and leave out reset and power > completely. Like I said above, the DT is considered an ABI and you'll have to maintain backward compatibility (ie, newer kernel running with older DT). Therefore, you won't be able to require a new clock, reset or power-domain later on for example. I guess the question I'm really asking is: since you don't really know how the hardware is integrated at the moment, why should we have that discussion *now*. It's really not suprising that you don't know yet, so I'm not sure why we need to rush in the bindings. Maxime
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