On Mon, Nov 17, 2014 at 10:46 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Monday 17 November 2014 09:01:02 Kevin Cernekee wrote: >> On Mon, Nov 17, 2014 at 4:16 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> Under arch/mips/bcm47xx I see a single mach type, but different builds >> for BMIPS3300 (R1/SSB) versus MIPS 74K (R2/BCMA). > > At least in Kconfig, the two are not mutually exclusive, so I assumed > you could enable them both at the same time. Ah right, bcm47xx_defconfig doesn't actually enable CONFIG_CPU_MIPS32_R2. So it will still run on R1 CPUs like BMIPS3300. On R2 systems it may lose a few optimizations/features. I suspect that BCM47xx could use the BMIPS multiplatform kernel, if somebody was willing to figure out how to convert board.c, leds.c, etc. >> > If you wanted to do that however, starting with BMIPS you'd have >> > to make it possible to define a new platform without the >> > arch/mips/include/asm/mach-bmips/ directory (this should be possible >> > already, so the hardest part is done), replace all global function >> > calls (arch_init_irq, prom_init, get_system_type, ...) with generic >> > platform-independent implementations or wrappers around per-platform >> > callbacks, and move the Kconfig section for CONFIG_BMIPS_MULTIPLATFORM >> > outside of the "System type" choice statement. >> >> Right. The other question is how much support for legacy non-DT >> bootloaders really belongs in a true multiplatform kernel, as this >> stuff gets hairy fast. > > Yes, that's why I suggested following PowerPC rather than ARM in this > regard. If you move the boot loader abstraction into the decompressor > instead of the platform code, you can avoid a lot of the problems. One possible complication: for BCM63xx/BCM7xxx (MIPS) there is no decompressor in the kernel. The firmware loads an ELF image into memory and jumps directly to kernel_entry.
