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

[Sean Anderson]

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.

> 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 at 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.

--Sean

> +		pr_err("Failed to restore hwpart to userdata\n");
> +}
> +
>  #if defined(CONFIG_FASTBOOT_MMC_BOOT_SUPPORT) || \
>  	defined(CONFIG_FASTBOOT_MMC_USER_SUPPORT)
>  static int fb_mmc_erase_mmc_hwpart(struct blk_desc *dev_desc)
> @@ -246,7 +252,7 @@ static void fb_mmc_boot_ops(struct blk_desc *dev_desc, void *buffer,
>  		if (blkcnt > dev_desc->lba) {
>  			pr_err("Image size too large\n");
>  			fastboot_fail("Image size too large", response);
> -			return;
> +			goto fail_restore_hwpart;
>  		}
>  
>  		debug("Start Flashing Image to EMMC_BOOT%d...\n", hwpart);
> @@ -257,7 +263,7 @@ static void fb_mmc_boot_ops(struct blk_desc *dev_desc, void *buffer,
>  			pr_err("Failed to write EMMC_BOOT%d\n", hwpart);
>  			fastboot_fail("Failed to write EMMC_BOOT part",
>  				      response);
> -			return;
> +			goto fail_restore_hwpart;
>  		}
>  
>  		printf("........ wrote %lu bytes to EMMC_BOOT%d\n",
> @@ -267,11 +273,15 @@ static void fb_mmc_boot_ops(struct blk_desc *dev_desc, void *buffer,
>  			pr_err("Failed to erase EMMC_BOOT%d\n", hwpart);
>  			fastboot_fail("Failed to erase EMMC_BOOT part",
>  				      response);
> -			return;
> +			goto fail_restore_hwpart;
>  		}
>  	}
>  
>  	fastboot_okay(NULL, response);
> +	return;
> +
> +fail_restore_hwpart:
> +	fastboot_mmc_select_default_hwpart(dev_desc);
>  }
>  #endif
>  
> @@ -630,6 +640,8 @@ void fastboot_mmc_flash_write(const char *cmd, void *download_buffer,
>  		write_raw_image(dev_desc, &info, cmd, download_buffer,
>  				download_bytes, response);
>  	}
> +
> +	fastboot_mmc_select_default_hwpart(dev_desc);
>  }
>  
>  /**
> @@ -694,6 +706,8 @@ void fastboot_mmc_erase(const char *cmd, char *response)
>  
>  	blks = fb_mmc_blk_write(dev_desc, blks_start, blks_size, NULL);
>  
> +	fastboot_mmc_select_default_hwpart(dev_desc);
> +
>  	if (blks != blks_size) {
>  		pr_err("failed erasing from device %d\n", dev_desc->devnum);
>  		fastboot_fail("failed erasing from device", response);
> diff --git a/include/mmc.h b/include/mmc.h
> index 027e8bcc73a6..cdd457a60a5b 100644
> --- a/include/mmc.h
> +++ b/include/mmc.h
> @@ -362,6 +362,7 @@ enum mmc_voltage {
>  /* The number of MMC physical partitions.  These consist of:
>   * boot partitions (2), general purpose partitions (4) in MMC v4.4.
>   */
> +#define MMC_PART_USERDATA	0
>  #define MMC_NUM_BOOT_PARTITION	2
>  #define MMC_PART_RPMB           3       /* RPMB partition number */
>  
> 
> ---
> base-commit: f5717231abad983b4d8f87db612ae60dec86cb1b
> change-id: 20221010-switch-hwpart-7fed7746db59
> 
> Best regards,
>