On 28 August 2014 12:13, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> 1) prom_init / plat_mem_setup >> These two functions are called in pretty much the same phase from the >> setup_arch (arch/mips/kernel/setup.c). >> Task: detect & register memory >> Requires: CPU type, maybe Broadcom chip ID (highmem support) >> Available: CPU type >> Not available: kmalloc, device_add (kobject) >> >> 2) arch_init_irq >> Called from the arch specific init_IRQ (arch/mips/kernel/irq.c) >> Task: setup bcma's MIPS core >> Requires: bcma bus MIPS core >> Available: kmalloc >> Not available: device_add (kobject) >> >> 3) plat_time_init >> Called from the arch specific time_init (arch/mips/kernel/time.c) >> Task: set frequency >> Requires: bcma bus ChipCommon core, nvram >> Available: kmalloc >> Not available: device_add (kobject) > > My impression is that all the information that you need in these early > three steps is stuff that is already meant to be part of DT. > This isn't surprising, because the bcm47xx serves a similar purpose > to DT, it's just more specialized. > > This duplication is a bit unfortunate, but it seems that just using > the respective information from DT would be easier here. > > Is any of the information you need early dynamic? It sounds that > for a given SoC, it should never change and can just be statically > encoded in DT. I'm not sure which info you exactly are talking about. I believe one SoC model always use the same CPU, ChipCommon, embedded wireless and PCIe + USB controllers. However amount of RAM, type of flash (serial vs. NAND), size of flash, booting method, NVRAM location, etc. all depend on vendor's choice. I think CPU speed could also depend on vendor choice. >> 4) At some point we need to register bcma devices, device_initcall can >> be used for that >> >> As you can see, we need access to the NVRAM quite early (step 3, >> plat_time_init, or even earlier), but device_add (platform >> devices/drivers) is not available then yet. So I'm afraid we won't be >> able to use this common way to write NVRAM driver. >> >> >> So there I want to present my plan for the NVRAM improvements. If you >> don't agree with any part of it, or you can see any better solution, >> please speak up! >> >> 1) I won't make nvram.c a platform driver. Instead I would like to >> make it less bcm47xx specific. I don't want to touch bcm47xx_bus in >> this file. Instead I want to add a generic function that will accept >> address and size of memory where NVRAM should be found. Then I'd like >> to move this file out of "mips" arch (drivers/misc/? >> drivers/bcma/nvram/?) and allow using it for bcm53xx. > > In general, I'd try to avoid adding any platform specific code on ARM > when it needs to run as something other than a device driver. > Moving the code out of arch/mips and making it more generic definitely > sounds good to me, but I'd prefer to have an actual platform_driver > for it. Sure, I didn't want to add NVRAM driver into arch/arm/ :) Can you see any solution for making NVRAM support a standard platform driver on MIPS and ARM? As I said, on MIPS we need access to the NVRAM really early, before platform devices/drivers can operate. >> 3) Above change (point 2) would require some small change in bcma. We >> would need 2-stages init: detecting (with kmalloc!) bus cores, >> registering cores. This is required, because we can't register cores >> too early, device_add (and the underlying kobject) would oops/WARN in >> kobject_get. > > Right. Could you do the bcma scan much later, at the time when > device_add works as well? Traditionally PCI has been a problem > since it had to be enabled really early, but that restriction > should be gone now, and we can actually probe it from a loadable > module. Take a look at "arch_init_irq" I described above. It needs access to the MIPS core (bcma bus contains many cores). To get access to this core (to know it exists and to get it mapped), I need to scan the bus. > On a global level, there is another choice, which is to do something > similar to the 'pxa-impedence-matcher' and the 'sunxi-babelfish': > These are two projects that implement a last-stage boot loader that > runs before the kernel and translates a platform-specific boot format > into standard DTB format. We could do the same for bcm53xx and > translate any nvram strings we know about into properties of device > nodes we already have, and copy all remaining strings into a > properties of the /chosen node. That way, we don't even need any > nvram driver for ARM, except a trivial one that provides raw > write access to user space for updating it. I think on bcm53xx early access to the NVRAM is less important, so this may be not such a big problem at all. -- Rafał
