On Thu, Jul 28, 2011 at 09:42:15PM +0200, Arnd Bergmann wrote: > On Thursday 28 July 2011 14:44:17 Nicolas Pitre wrote: > > > > > > We could even embed the printch() function body into the DT if we > > > wanted to make the kernel's job even simpler. Realistic implementations > > > of this function are tiny, so this shouldn't be too cumbersome. > > > That really seems an abuse of the DT though, since this goes beyond > > > just describing the hardware. > > > > Well... I'm not entirely against the idea. This could be seen as the > > most efficient way to describe how to output a character over some > > serial device for the given hardware. The danger is that some vendors > > might be tempted to abuse that idea by stuffing BIOS-like services in > > there that the kernel would have to cope with. > > I thought about this before, but then remembered the horrors of RTAS > on powerpc and quickly discarded the idea. There are so many ways in > which this can backfire: > > * People putting entire closed source device drivers into the firmware > and letting the kernel call that > > * changing linkage convention in the kernel in a way that doesn't > work with the code: thumb2, big-endian, oabi, ... > > * sharing (part of) a device tree on SoC platforms that have > multiple CPU architectures: TI C6x, qualcomm hexagon, freescale ppc, > xilinx microblaze, openrisc > > * subtle resource conflicts between the embedded code and other > device drivers, e.g. using the same IRQ, registers or pins. > > Doing it just for printch sounds harmless at first, but I think > we should say no to this solution whenever it comes up, > so it doesn't have the chance to grow into something evil.
That sounds sensible to me; I was just throwing ideas about, really. The embedded code idea would work for this, but doesn't feel like the correct solution -- as you say, it invites future breakages and abuses, as well as going against the basic design principles of devicetree. I guess the flipside is that it would be good to have a way to extract specific bits of information from the device tree really early during boot. We don't need this yet, but it could be worth exploring it next week. Cheers ---Dave _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
