Re: [PATCH] fastboot: mmc: switch to user hwpart after erase/flash

Sean Anderson
2022-10-11T15:52:40Z

On 10/11/22 8:07 AM, Mattijs Korpershoek wrote:
> Hi Sean,
>
> Thank you for your review.
>
> On Mon, Oct 10, 2022 at 11:38, Sean Anderson <sean.anderson@seco.com> wrote:
>
>> On 10/10/22 4:05 AM, Mattijs Korpershoek wrote:
>>> Before erasing (or flashing) an mmc hardware partition, such as
>>> mmc0boot0 or mmc0boot1, we select it using blk_dselect_hwpart().
>>>
>>> However, we don't select back the normal (userdata) hwpartition
>>> afterwards.
>>>
>>> For example, the following sequence is broken:
>>>
>>> $ fastboot erase mmc2boot1 # switch to hwpart 1
>>> $ fastboot reboot bootloader # attempts to read GPT from hwpart 1
>>>
>>>> writing 128 blocks starting at 8064...
>>>> ........ wrote 65536 bytes to 'mmc0boot1'
>>>> GUID Partition Table Header signature is wrong: 0xFB4EC30FC5B7E5B2 != 0x5452415020494645
>>>> find_valid_gpt: *** ERROR: Invalid GPT ***
>>>> GUID Partition Table Header signature is wrong: 0x0 != 0x5452415020494645
>>>> find_valid_gpt: *** ERROR: Invalid Backup GPT ***
>>>> Error: mmc 2:misc read failed (-2)
>>>
>>> The GPT is stored in hwpart0 (userdata), not hwpart1 (mmc0boot1)
>>
>> This seems like a problem with your boot script. You should run `mmc dev
>> ${mmcdev}` (and `mmc rescan`) before trying to access any MMC
>> partitions. This is especially important after fastbooting, since the
>> partition layout (or active hardware partition) may have changed.
>
> I don't think I can fix this in my boot script.
> My boot script runs => fastboot usb 0 which will start a loop to receive
> fastboot commands from the host.
>
> The full u-boot env i'm using is in include/configs/meson64_android.h
>
> This loop will go on until "fastboot reboot <reboot_reason>" is called.
>
> I do can "work around" this by using the following fastboot sequence:
> $ fastboot erase mmc2boot1
> $ fastboot oem format # switch backs to hwpart 0 (USER)
> $ fastboot reboot bootloader
>
> But that's not a good option to me. From a user's perspective, it should
> not matter in which order we issue fastboot commands to the board.
>
> Maybe I should fix bcb.c instead to make sure that it selects hwpart0
> before reading/writing into the bcb partition ?

Yes. The bcb command should be using something like
part_get_info_by_dev_and_name_or_num instead of using its own bespoke
parsing. Unfortunately, command syntax is part of the API, but at the
very least you can fall back to something sane if argv[2] ("devnum")
doesn't parse as an int (aka it's the ifname).

--Sean

>>
>>> As the blk documentation states:
>>>> Once selected only the region of the device
>>>> covered by that partition is accessible.
>>>
>>> Add a cleanup function, fastboot_mmc_select_default_hwpart() which
>>> selects back the default hwpartition (userdata).
>>>
>>> Note: this is more visible since
>>> commit a362ce214f03 ("fastboot: Implement generic fastboot_set_reboot_flag")
>>> because "fastboot reboot bootloader" will access the "misc" partition.
>>>
>>> Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
>>> ---
>>> This fix has been used for over a year in the AOSP tree at [1]
>>>
>>> [1] https://android.googlesource.com/device/amlogic/yukawa/+/c008ddaec0943adda394b229e83e147f6165773c
>>> ---
>>> drivers/fastboot/fb_mmc.c | 20 +++++++++++++++++---
>>> include/mmc.h | 1 +
>>> 2 files changed, 18 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/fastboot/fb_mmc.c b/drivers/fastboot/fb_mmc.c
>>> index 033c510bc096..dedef7c4deb1 100644
>>> --- a/drivers/fastboot/fb_mmc.c
>>> +++ b/drivers/fastboot/fb_mmc.c
>>> @@ -199,6 +199,12 @@ static void write_raw_image(struct blk_desc *dev_desc,
>>> fastboot_okay(NULL, response);
>>> }
>>>
>>> +static void fastboot_mmc_select_default_hwpart(struct blk_desc *dev_desc)
>>> +{
>>> + if (blk_dselect_hwpart(dev_desc, MMC_PART_USERDATA))
>>
>> If you really want to do this, we shoud save the current partition and
>> restore if after fastbooting. Always switching to hardware partition 0
>> is just as broken as the current behavior.
>
> ACK. This patch just replaces one broken behaviour by another one. I
> will see if I can save the hardware partition state instead or patch the
> bcb command.
>
>
>>
>> --Sean
>>
>