[U-Boot] DA850evm SPI Flash Partitions between Linux and U-boot are Inconsistent

[Sekhar Nori]

On Tuesday 29 August 2017 03:29 PM, Adam Ford wrote:
> On Tue, Aug 29, 2017 at 4:13 AM, Sekhar Nori <nsekhar at ti.com> wrote:
>> Hi Adam,
>>
>> On Sunday 27 August 2017 08:31 PM, Adam Ford wrote:
>>> I was trying to enable MTD Partitions to make loading the Kernel and
>>> FS easier from within U-Boot
>>>
>>> The da850evm spi-flash partitions in Linux show
>>>
>>> "U-Boot-SPL" @ offset 0, size 64K
>>> "U-Boot"; @ offset 0x00010000, size 512K
>>> "U-Boot-Env"; @ offset 0x00090000
>>
>> According to board/davinci/da8xxevm/README.da850, we support AIS image
>> format for SPI boot. This is a single image containing SPL and U-Boot.
>>
>> Given this, I think having separate partitions for SPL and U-Boot does
>> not make sense since thats not how its going to be used.
> 
> That's what I was thinking too, but I wasn't sure if someone had split
> SPL somehow to make it possible to update U-Boot via Linux or U-Boot
> itself.
>>
>>>
>>> However U-Boot shows the following:
>>>
>>> CONFIG_SYS_SPI_U_BOOT_OFFS 0x8000 which would make the SPL partition 32K.
>>> CONFIG_SYS_SPI_U_BOOT_SIZE      0x40000 and the size of U-boot 256K
>>> instead of 512k.
>>>
>>> CONFIG_ENV_SIZE                 (64 << 10)
>>> CONFIG_ENV_OFFSET           (512 << 10) which is 0x80000 instead of
>>> Linux's 0x90000
>>>
>>> It seems to me like the U-Boot and Linux should try and synchronize
>>> their partitions tables.
>>
>> Right.
>>
>>> For people who want to burn Linux into the SPI flash it seems there
>>> there should be some consistency.  I tried making the U-boot settings
>>> match the Linux ones, but it seems to hang between SPL and U-Boot, so
>>> I think the U-Boot offset in Linux might need to match U-Boot.  Can
>>> you guys make some recomendations as to which is correct?
>>
>> I have not tried it, but looks like the partitions we need are
>>
>> "SPL/U-Boot AIS" @ offset 0, size 512K
>> "U-Boot Environment" @ offset 512K, size 64K
> 
> I was thinking the same thing.
> 
>> "Kernel/Spare" @ offset 576K, size 7552K
>> "Mac Address" @ offset 8128K, size 64K (read only)
> 
> If U-Boot reads the MAC address from its environmental variables
> instead of using up an entire 64K for what conceivably is 6 bytes,
> could we free up this space to help grow the Kernel/Spare space?

If environment sector is erased, the mac address needs to be restored
from SPI flash. Thats why I think it needs to remain as a read-only
partition. Also, its just 64K more space, not sure if it will make a big
difference in the overall scheme of things.

>> With an 8M flash, I think its futile to try to fit a modern filesystem
>> on the flash.
>>
>> If you are using DT boot, we cannot really change the partitions in
>> device-tree because of DT backward-compatibility requirements. But we
>> can fix da850evm_spiflash_part[] table in
>> arch/arm/mach-davinci/board-da850-evm.c.
> 
> Wouldn't having two different partition tables between da850-evm.c and
> the DT cause confusion down the road?  With DT being the future, why
> would we not try to eliminate any custom board files with just a
> single common davinci board file + board specific DT?

Thats ideal yes. But there is a lot of support in the da850-evm board
file which does not have a DT equivalent yet. Thats why I have kept the
board file around.

>> To help DT boot, we can pass fixed up mtdparts through environment
>> variables. Something like what is done in 3f18ff07c81b ("ARM: keystone:
>> Pass SPI MTD partition table via kernel command line").
> 
> This was ultimately was I was wanting to do.  For some of the OMAP3
> boards, removing the partition tree was accepted since the partition
> info was passed to the kernel.  If we did this for DA850, we could
> simply elimiate the partition info in the Kernel (like some of the
> omap3 boards) and let the partition maps be defined by U-Boot would
> would guarantee consistency between them.

Actually, thinking a bit more, we cannot change the partition
information in kernel at all since that means loss of data for anyone
updating just the kernel.

We can however, pass updated kernel command line arguments in U-Boot so
anyone updating the bootloader and erasing the environment sector gets
updated partition information. This is likely to be the case where
entire flash is being re-written and loss of data is not a concern.

Thanks,
Sekhar