On 28 August 2014 17:32, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Thursday 28 August 2014 14:37:54 Rafał Miłecki wrote:
>> To make booting possible, flash content is mapped to the memory. We're
>> talking about read only access. This mapping allows CPU to get code
>> (bootloader) and execute it as well as it allows CFE to get NVRAM
>> content easily. You don't need flash driver (with erasing & writing
>> support) to read NVRAM.
>
> Ok. Just out of curiosity, how does the system manage to map NAND
> flash into physical address space? Is this a feature of the SoC
> of the flash chip?
I don't know exactly. Many (all?) device with BCM4706 SoC have two
flashes. Serial flash (~2 MiB) with bootloader + nvram and NAND flash
with the firmware. However Netgear WNR3500Lv2 (based on BCM47186B0)
has only a NAND flash.
> I guess for writing you'd still use the full MTD driver, right?
That's right. This is why I wrote about "talking about read only access".
>> Depending on the boot flash device, content of flash is mapped at
>> different offsets:
>> 1) MIPS serial flash: SI_FLASH2 (0x1c000000)
>> 2) MIPS NAND flash: SI_FLASH1 (0x1fc00000)
>> 3) ARM serial flash: SI_NS_NORFLASH (0x1e000000)
>> 4) ARM NAND flash: SI_NS_NANDFLASH (0x1c000000)
>>
>> So on my ARM device with serial flash (connected over SPI) I was able
>> to get NVRAM header this way:
>>
>> void __iomem *iobase = ioremap_nocache(0x1e000000, 0x1000000);
>> u8 *buf;
>>
>> buf = (u8 *)(iobase + 0xff0000);
>> pr_info("[NVRAM] %02X %02X %02X %02X\n", buf[0], buf[1], buf[2], buf[3]);
>>
>> This resulted in:
>> [NVRAM] 46 4C 53 48
>>
>> (I hardcoded 0xff0000 above, normally you would need to try 0x10000,
>> 0x20000, 0x30000 and so on...).
>
> Does that mean the entire 0x1e000000-0x1f000000 area is mapped to
> the flash and you are looking for the nvram in it, or that you don't
> know where it is?
The correct algorithm would be:
for (off = 0; off < SOME_LIMIT; off += 0x10000) {
buf = (u8 *)(iobase + off);
if (buf[0] == 0x46 && buf[1] == 0x4C) {
pr_info("NVRAM found at 0x%X offset\n", off);
break;
}
}
--
Rafał
