[U-Boot] [U-Boot, v2] env: mmc/fat/ext4: make sure that the MMC sub-system is initialized before using it

[Faiz Abbas]

Hi,

On Sunday 25 February 2018 07:18 PM, Tom Rini wrote:
> On Sun, Feb 25, 2018 at 09:53:10AM +0100, Wolfgang Denk wrote:
>> Dear Tom Rini,
>>
>> In message <20180224215325.GQ4311 at bill-the-cat> you wrote:
>>>
>>>> Why do you ignore this NAK, and why do you add this patch so late in
>>>> the release cycle anyway?
>>>
>>> Sorry, didn't v2 address your concerns?  We don't initialize the device
>>> because maybe we'll have env there, we initalize mmc because we need to
>>> check that it is there.  Thanks!
>>
>> No, it does not.  As is, we initialize MMC in the EXT4 code (in
>> env_ext4_load()). If we go that route, we would have to add similar
>> init calls to all other file systemn load routines as well.
>>
>> This does not make sense to me.  This pollutes the code with
>> unrelated things - file system code should not depend on any
>> underlaying driver suport.  It increases code size, makes the code
>> harder to maintain (if you need to change this, there is good
>> chances to forget the same change in other file systems), and there
>> is a good chance that in the end you will initialzie MMC even if you
>> don't use it.
>>
>> We should keep the code clean and orthogonal.  Driver init code has
>> no place in file system code.
>>
>> If needed, the drivers have to make sure to auto--initialize on
>> first access.
>>
>> I hold my NAK on this patch.  It is the wrong thing to do.
> 
> I think you have this a little bit wrong.  But, it's also where we are
> with the DM conversion.  This _is_ the first place we're trying to
> access the MMC.  And it's not in the filesystem code, it's in the
> environment code.
> 
> That said, Faiz, what exactly is the failure sequence (and hardware)?
> Thanks!
>


The failure happens in SPL when booting from a non-MMC device (say NAND)
and environment is in MMC. I have seen it in am335x_evm (with NAND and
ethernet boot mode) and in dra7xx_evm (with qspi boot mode).

The failure sequence is as follows:

1. spl_start_uboot() in the appropriate board file calls env_load().

2. Since ENV_IS_IN_FAT and CONFIG_ENV_FAT_INTERFACE=mmc, env_fat_load()
eventually leads to a call to find_mmc_device() in
drivers/mmc/mmc_legacy.c or mmc-uclass.c

3. Since the mmc devices have not been probed (by a call to
mmc_initialize()), SPL is not able to get the environment and I get this
warning message:

*** Warning - No MMC card found, using default environment


Note: In case of legacy mode (CONFIG_BLK is not enabled), SPL crashes
because of dereferencing a NULL pointer (mmc_devices) in find_mmc_device().


Thanks,
Faiz