Re: Kernel 3.10.31 and SD card numbering and boot scripts

[Eric Nelson <eric.nelson@boundarydevices.com>]

Hi Otavio,

On 10/10/2014 05:23 AM, Otavio Salvador wrote:
> On Thu, Oct 9, 2014 at 10:45 PM, Eric Nelson
> <eric.nelson@boundarydevices.com> wrote:
>> Thanks for the feedback Otavio,
>>
>> On 10/09/2014 06:18 PM, Otavio Salvador wrote:
>>> On Thu, Oct 9, 2014 at 9:00 PM, Eric Nelson
>>> <eric.nelson@boundarydevices.com> wrote:
>>>> The 3.10.31 kernel contains a nifty bit of code from Sascha Hauer
>>>> that addresses the question of SD card numbering (device naming)
>>>> quite well:
>>>>
>>>>         http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/commit/drivers/mmc/card/block.c?h=imx_3.10.31_1.1.0_beta&id=5f9447e5d97060207c4742d5a06e5548de45972d
>>>>         https://www.mail-archive.com/linux-mmc@vger.kernel.org/msg26472.html
>>>>
>>>> Unfortunately, it also changes the requirements for the kernel
>>>> command-line and breaks our boot scripts.
>>>
>>> Yes.
>>>
>>>> This is probably a good time to ask a related question about
>>>> where we're keeping boot scripts.
>>>>
>>>> We have been compiling boot scripts out of our U-Boot tree
>>>> from a Yocto-specific "6x_bootscript-yocto.txt" that implements
>>>> the conventions of the Freescale Community BSP (kernel in
>>>> the root of partition 1 and rootfs in partition 2).
>>>>
>>>> Since boot scripts have dependencies on a lot of things, it's
>>>> not clear to me that they belong in the U-Boot source treet
>>>> and that a Yocto-specific boot script really belongs directly
>>>> in the Yocto tree somewhere.
>>>>
>>>> Since a Yocto build knows about the PREFERRED_VERSION of the
>>>> kernel, it would be straightforward to have multiple versions
>>>> of a boot script.
>>>>
>>>> Otherwise, we'd need to place a couple of versions in the
>>>> U-Boot tree:
>>>>         6x_bootscript-yocto.txt
>>>>         6x_bootscript-yocto-after-3.10.17.txt
>>>> and we'd also need some logic in u-boot-script-boundary.bb
>>>> to choose between them.
>>>>
>>>> Before crafting a patch to do this, I'd like to get some feedback.
>>>
>>> It is harder than it seems to be. The providing system does not track
>>> versions so you'd need to do some "uglyness" to make this work.
>>>
>>
>> I haven't tried, but it seems generally useful to allow
>> conditionals based on kernel versions in Yocto/OE and I'm
>> surprised that there isn't a stock way of doing this.
> 
> It would be indeed however there are some complexities as package feed
> upgrade path and other details which makes this very complex.
> 
> As I said, I think this is technically possible to be done but will
> require some 'hacks'.
> 
>>> Personally I think it is easier to address this on the bootscript
>>> itself using the setexpr command in U-Boot and with the REGEX config
>>> enabled. So you could try to match the kernel version on it somehow.
>>>
>>> Not sure if we have a command to 'ask' for the kernel version loaded though...
>>>
>>
>> Not currently.
>>
>> Using a root=PARTUUID=blah would also be nice and might allow the same
>> command-line on multiple kernel versions.
>>
>> Unfortunately, this doesn't seem to work:
>>         https://github.com/boundarydevices/linux-imx6/blob/boundary-imx_3.10.31_1.1.0_beta/init/do_mounts.c#L213
> 
> The problem with the UUID is because we need to inject it during
> rootfs generation and it'd not be in the initial environment, so an
> 'env default -f -a' would make the system not bootable. In your case,
> as you use the script in a partition it is more doable but it'd not be
> an generic solution.
> 

If the kernel could accept a PARTUUID parameter, the boot script
could potentially produce it, but that doesn't seem to be an
immediate option.

Regards,


Eric