On Wed, 17 Jan 2018, PrasannaKumar Muralidharan wrote: > > Yes I would like to do so. Loongson-2K have a limited support with DeviceTree > > (OpenFirmware) by U-Boot bootloader. Later SoC chips will also support DT as I > > know. > > But Loongson-1 series and 2E/2F only have leagcy boot support, no EFI, no DT, > > even not all bootloader support machtype (in boot cmdline). That's why we want > > to creat different entries for these platforms. > > It is possible to use DT even if boot loader does not supply it. The > dtb can be append to the kernel and kernel can be configured to pick > it up. Problems start when such DTB disagrees with how the system has actually been configured. I once had to go through pains in the past when upgrading the kernel on a Freescale board where different versions of the firmware set up resources differently and the DTS supplied with the kernel assumed the most recent one. I had to port random DTS updates to the old version to keep the old resource assignment while making the result understandable to the new kernel as the syntax evolved. And I think I may not have got everything right as e.g. I couldn't access the PATA CD-ROM the system was equipped with after the upgrade anymore (fortunately I didn't need it, so I just ignored the problem). In case someone suggests I could have upgraded the firmware: well, technically yes, but first that would cut the route back to the previous kernel version if the new one wasn't usable enough, and second the board was somewhere in a rack in a data centre across the pond, so no, I didn't dare bricking it. So yes, having a DTB integrated with the kernel is certainly an option, but a lot of care has to be taken to make it an aid rather than a burden. FWIW, Maciej
