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

[Adam Ford]

On Tue, Aug 29, 2017 at 8:05 AM, Adam Ford <aford173 at gmail.com> wrote:
> On Tue, Aug 29, 2017 at 6:41 AM, Sekhar Nori <nsekhar at ti.com> wrote:
>> 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.
>>
> That makes sense to me.
>
> I'll send a U-Boot patch marked RFC later today with the MTD stuff
> enabled in U-Boot and changes to the bootargs to pass the MTD
> information to Linux.
>

I have a patch ready for review for U-Boot, but I had to make a few
changes to the davinci_all_defconfig to get the MTD partitions to map
correctly:

-CONFIG_MTD=m
+CONFIG_MTD=y
 CONFIG_MTD_TESTS=m
+CONFIG_MTD_CMDLINE_PARTS=y
+CONFIG_MTD_OF_PARTS=m


Are you OK with that?  If so, I'll push a formal patch to Linux and
then submit a subsequent patch for U-Boot marked RFC with MTD parts
and CMD stuff enabled to pass the MTD partition info to Linux.

Currently, I have it defined as:
mtdparts=spi0.0:512k(u-boot.ais),64k(u-boot-env),7552k(kernel-spare),64k(MAC-Address)

Does that work for you?

>
>> Thanks,
>> Sekhar

adam