On 28 August 2014 13:02, Arnd Bergmann [off-list ref] wrote:

On Thursday 28 August 2014 12:47:29 Rafał Miłecki wrote:

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On 28 August 2014 12:13, Arnd Bergmann [off-list ref] wrote:

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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.

But those would also be present in DT on ARM, right?

Well, that depends. Hauke was planning to put info about flash in DT.
Me on the other hand suggested reading info about flash from the
board. See my reply:
https://www.mail-archive.com/devicetree@vger.kernel.org/msg39365.html

My plan was to use patch like
[PATCH] bcma: get & store info about flash type SoC booted from
http://www.spinics.net/lists/linux-wireless/msg126163.html
(it would work on both: MIPS and ARM)
and then:

switch (boot_device) {
case BCMA_BOOT_DEV_NAND:
    nvram_address = 0x1000dead;
    break;
case BCMA_BOOT_DEV_SERIAL:
    nvram_address = 0x1000c0de;
    break;
}

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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/ :)

What I meant is that I'd prefer to not even call a probe function
for this driver from arch/arm. I may have misunderstood what you meant
though.

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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.

I think it would make sense to have a common driver that has both
an 'early' init part used by MIPS and a regular init part used by
ARM and potentially also on MIPS if we want. Most of the code can
still be shared.

OK, now it's clear what you meant.
The thing is that we may want to call probe function from
drivers/bcma/main.c. I think we never meant to call it directly from
arch code. This code in drivers/bcma/main.c is used on both: MIPS and
ARM. So I wonder if there is much sense in doing it like
#ifdev MIPS
bcm47xx_nvram_init(nvram_address);
#endif
#ifdef ARM
nvram_device.resource[0].start = nvram_address;
platform_device_register(nvram_device);
#endif

What do you think about this?

-- 
Rafał