[U-Boot] [PATCH 2/2] mmc: restore capacity when switching to partition 0

[Peter A. Bigot <pab@pabigot.com>]

On 09/03/2014 10:48 AM, Stephen Warren wrote:
> On 09/02/2014 05:31 PM, Peter A. Bigot wrote:
>> The capacity and lba for an MMC device with part_num 0 reflects the
>> whole device.  When mmc_switch_part() successfully switches to a
>> partition, the capacity is changed to that partition.  As partition 0
>> does not physically exist, attempts to switch back to the whole device
>> will indicate an error, but the capacity setting for the whole device
>> must still be restored to match the partition.
>
>> diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
>
>> @@ -594,10 +594,15 @@ int mmc_switch_part(int dev_num, unsigned int 
>> part_num)
>>       ret = mmc_switch(mmc, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_PART_CONF,
>>                (mmc->part_config & ~PART_ACCESS_MASK)
>>                | (part_num & PART_ACCESS_MASK));
>> -    if (ret)
>> -        return ret;
>>
>> -    return mmc_set_capacity(mmc, part_num);
>> +    /*
>> +     * Set the capacity if the switch succeeded or was intended
>> +     * to return to representing the raw device.
>> +     */
>> +    if ((ret == 0) || ((ret == -ENODEV) && (part_num == 0)))
>> +        ret = mmc_set_capacity(mmc, part_num);
>> +
>> +    return ret;
>>   }
>
> I think this wouldn't be needed without patch 1/2, since without that 
> patch, no partition switching should ever happen if HW partitions 
> don't exist, and hence this patch shouldn't be required.

Not so.

In SPL mode, the mmc device passed in to the environment code is set up 
for partition 0.  In the failure case, u-boot is configured to expect an 
environment in partition 2, and so invokes mmc_switch_part to go to 
partition 2 to see if it's a valid partition.  In my case that fails 
because the partition size is zero, but regardless the mmc_switch_part 
back to mmc->part_num fails because the mmc_switch() call rejects the 
attempt with an error.

Without this second patch, you end up with mmc->part_num left at zero 
but the capacity/lba fields configured for partition 2 which does not 
exist and has size zero, and SPL is unable to locate u-boot.img to continue.

Please review the details in the meta-ti discussion.

I'll respond to the comments on patch 1 separately.

Peter