Hi, On Thu, 2017-10-19 at 16:54 +0200, Philipp Zabel wrote: > Hi Laurent, > > On Thu, 2017-10-19 at 16:39 +0300, Laurent Pinchart wrote: > > 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) ? > > Because the "display-subsystem" node does not represent a real device, > it's just there to probe the driver that stitches all the DISP > components together. > > > > 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 > > ? > > All devices in the 0x14000000 - 0x14ffffff memory range are part of the > MMSYS system. That includes the MMSYS control or system configuration > block at 0x14000000 - 0x14000fff as well as all the related MDP (media > data path) and DISP (display data path) blocks that follow. The DISP > blocks are purely display related, while the MDP blocks implement > implement mem2mem functions like scaling and conversion. > > > > > 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 ? > > The MMSYS control block provides clocks for the DISP (display data path) > and MDP (multimedia data path) blocks, as well as the routing between > them, but not to anything outside of the MMSYS system. According to register table of mediatek x20 mmsys [1] and Philipp's statement, I think mmsys is neither clock-controller nor display controller. It's a combination of multiple function. The four major function is display's clock-control, mdp's clock-control, display's routing, and mdp's routing. So we have two choice: 1) Centralize these multiple function control inside mmsys device: This means there is only a mmsys device which contains function of clock-control, display, and mdp. 2) Separate these multiple function to different device: mmsys is the major device which owns the register resource but does nothing. The function is controlled by three virtual device: mmsys-clock-controller, display-controller, and mdp-controller. I prefer 2) because these function seems independent. Regards, CK [1] https://www.96boards.org/documentation/ConsumerEdition/MediaTekX20/AdditionalDocs/ > > regards > Philipp -- 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
