Hi Philipp, On Thursday, 19 October 2017 16:01:54 EEST Philipp Zabel wrote: > On Thu, 2017-10-19 at 13:26 +0200, Matthias Brugger wrote: > > In theory the MMSYS device tree identifier is matches twice, by the clk > > driver and the DRM subsystem. But the kernel only matches the first > > driver for a device (clk) and discards the second one. This breaks > > graphics on mt8173 and most probably on mt2701 as well. > > > > MMSYS in Mediatek SoCs has some registers to control clock gates (which is > > used in the clk driver) and some registers to enable the differnet blocks > > of the display subsystem. The kernel uses the binding to load the central > > comoponent of the distplay subsystem, which in place probes all the other > > components and enables the present ones in the MMSYS. > > > > We found us with the problem, that we need to change and therefor break > > one > > of the two bindings, or the DRM one or the clock driver one. > > > > Apart from that the DRM subysystem does access the MMSYS registers via > > relaxed reads/writes. But the it should to so via regmap, as the > > registers are shared. > > > > Possible solutions: > > 1) We add a new mediatek,mt8173-mmsys-clk node, which lives as a > > simple-mfd under the actual mmsys node. We change the clock driver to > > probe on this binding. This would make sense as the clock gate register > > live completly in the MMSYS configuration registers. > > The reason why the drm driver matches against the mmsys node in the > first place is that we wanted to avoid 2). Why did you want to avoid 2) ? > Also, mmsys is not a pure clock controller, as it also contains the > display path configuration in its register space. Which makes the mmsys related to display, but more in a syscon (combining clocks and routing, and I assume other miscellaneous features that wouldn't fit nicely in the other display-related IP cores) way than actually being part of the display subsystem. Or does mmsys only provide display-related features ? > > 2) As the nodes of the DRM subsystem just need some of the registers of > > MMSYS we add a new binding mediatek,mt8173-dispsys which probes the > > central component of the DRM system. It has only a handle to mt8173-mmsys > > to access the registerspace via regmap functions. > > > > In this patchset I implemented 2). Please take into account, that this is > > a RFC. I had no time to actually test the verison on real HW. Some of the > > register accesses should be done using regmap_update instead of > > regmap_read + regmap_write. > > > > This RFC shall only show how solution 2) would look like. We can use it as > > discussion to see how we circumvent the actual situation. > > Or we could leave the bindings untouched and create one platform device > from the other or even set up the clocks from the drm driver? Does mmsys provide features (such as clocks) to non-display IP cores ? -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
