Hi Andrzej, On Thursday, 5 April 2018 14:28:51 EEST Andrzej Hajda wrote: > On 05.04.2018 12:28, Laurent Pinchart wrote: > > On Wednesday, 4 April 2018 11:41:05 EEST Carsten Behling wrote: > >>> Hi, > >>> > >>> I would like to write a DRM bridge driver that is an I2C device and a > >>> DRM MIPI DSI device. > >>> > >>> It looks like that both - 'i2c-core.c: of_i2c_register_devices' and > >>> 'drm_mipi_dsi.c: mipi_dsi_host_register' are registering their devices > >>> by iterating over devicetree child nodes with > >>> for_each_available_child_of_node. > >>> > >>> Since I can't make the bridge a child node of both, I don't know how to > >>> resolve it. > >> > >> Found the answer myself. adv7533 driver is a good example. Devicetree > >> exists for qcom apq8016-sbc. No need to make the bridge a MIPI DSI child > >> node. > > > > This is an issue that has largely been ignored so far in Linux. Both DT > > and the Linux kernel device model organize devices in a tree structure > > based on the control buses. Devices that are connected to multiple control > > buses haven't been taken into account in the design and are thus hard to > > support. > > > > As you may know, DSI can work in command mode or data mode. In data mode > > the DSI bus is only use to transfer video data, while in command mode it > > is also used to control the device (reading and writing registers). > > I am not sure what you mean by data and command mode. MIPI DSI specs > says about video and command mode - modes to transfer video data. In > both cases DSI can be used to control the device.
Sorry, I meant pure video mode, when a panel only uses DSI to receive video data but handles all control communication through a separate control bus. > > A DSI device operating in data mode and controlled through I2C isn't a > > problem, as there's a single control bus in that case. The device should > > be a child of the I2C controller in DT, and will be instantiated through > > of_i2c_register_devices(). A DSI device operating in command mode without > > any other control bus isn't a problem either, it will be a child of the > > DSI master in DT, and will bee instantiated through > > mipi_dsi_host_register(). > > > > A DSI device operating in command mode that also require configuration > > through a separate control bus (such as I2C, but also SPI) is much more > > problematic to support. Fortunately those devices are rare. Hopefully > > your device won't fall in this category. If it does, we can discuss how > > to best support it. > > As you have already found adv bridge is a good example. It is not clear > from the emails if DSI is used only to send video, or also to control? > And if to control, is it used to pass only specific commands > or can be used as alternative to i2c interface? Carsten, could you please provide more information about the panel you're using ? -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
