On 28.08.2018 13:47, Thierry Reding wrote: > On Mon, Aug 20, 2018 at 10:35:54PM +0300, Dmitry Osipenko wrote: >> On 20.08.2018 22:27, Dmitry Osipenko wrote: >>> On 20.08.2018 22:12, Rob Herring wrote: >>>> On Sat, Aug 18, 2018 at 06:54:17PM +0300, Dmitry Osipenko wrote: >>>>> Splitting GART and Memory Controller wasn't a good decision that was made >>>>> back in the day. Given that the GART driver hasn't ever been used by >>>>> anything in the kernel, we decided that it will be better to correct the >>>>> mistakes of the past and merge two bindings into a single one. In a result >>>> >>>> As a result... >>>> >>>>> there is a DT ABI change for the Memory Controller that allows not to >>>>> break newer kernels using older DT by introducing a new required property, >>>>> the memory clock. Adding the new clock property also puts the tegra20-mc >>>>> binding in line with the bindings of the later Tegra generations. >>>> >>>> I don't understand this part. It looks to me like you are breaking >>>> compatibility. The driver failing to probe with an old DT is okay? >>> >>> Yes, DT compatibility is broken. New driver won't probe/load with the old DT, >>> that's what we want. >>> >>>> OS's like OpenSUSE use new DTs with older kernel versions, so you should >>>> consider how to not break them as well. I guess if all this is optional >>>> or has been unused, then there shouldn't be a problem. >>> >>> That's interesting.. Memory Controller isn't optional, I guess we could change >>> compatible to "nvidia,tegra20-mc-gart".bled in kernels config by >> default and driver is functional, but it's okay >> >> * I meant it's not optional in a sense that it's enaif MC driver will stop to probe >> with older kernels as it is used only for reporting memory errors. > > Yeah, we don't really regress at runtime. The errors reported by the > current driver are very rare, and even if you encounter them, they're > pretty cryptic, so I think this is one of the exceptional cases where > breaking the ABI "for the greater good" is acceptable. It's now became apparent that factoring out EMC from MC isn't a good idea too because MC need to interact with EMC and probably vice versa. Looks like we should consider restructuring MC for all Tegra's.
