Tabi Timur-B04825 <B04825@xxxxxxxxxxxxx> wrote: >On Mon, Nov 5, 2012 at 2:40 PM, Grant Likely ><grant.likely@xxxxxxxxxxxx> wrote: > >> Jane is building custom BeagleBone expansion boards called 'capes'. >She >> can boot the system with a stock BeagleBoard device tree, but >additional >> data is needed before a cape can be used. She could replace the FDT >file >> used by U-Boot with one that contains the extra data, but she uses >the >> same Linux system image regardless of the cape, and it is >inconvenient >> to have to select a different device tree at boot time depending on >the >> cape. > >What's wrong with having the boot loader detect the presence of the >Cape and update the device tree accordingly? We do this all the time >in U-Boot. Doing stuff like reading EEPROMs and testing for the >presence of hardware is easier in U-Boot than in Linux. > >For configurations that can be determined by the boot loader, I'm not >sure overlays are practical. >From the discussion in the previous thread, I'm sufficiently convinced that it is an important use case. I certainly disagree with the assertion that it is always easier to do it in U-Boot. Sometimes the kernel is the better place. > >> Nigel is building a real-time video processing system around a MIPS >SoC >> and a Virtex FPGA. Video data is streamed through the FPGA for post >> processing operations like motion tracking or compression. The FPGA >is >> configured via the SPI bus, and is also connected to GPIO lines and >the >> memory mapped peripheral bus. Nigel has designed several FPGA >> configurations for different video processing tasks. The user will >> choose which configuration to load which can even be reprogrammed at >> runtime to switch tasks. > >Now this, on the other hand, makes more sense. If the hardware >configuration is literally user-configurable, then okay. However, I'm >not sure I see the need to update the device tree. The device tree is >generally for hardware that cannot be discovered/probed by the device >driver. If we're loading a configuration from user space, doesn't the >driver already know what the hardware's capabilities are, since it's >the one doing the uploading of a new FPGA code? Not if the driver is only responsible for loading the bitstream. There is already a xilinx driver that does things this way. > Why not skip the >device tree update and just tell the driver what the new capabilities >are? How? What format will that data be in if not device tree? g. -- Sent from my Android phone with K-9 Mail. Please excuse my brevity. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
