Downstream NVIDIA bootloader provides gpt_sector=<sector> kernel command
line option to the kernel. This option should instruct the GPT partition
parser to look at the specified sector for a valid GPT header if the GPT
is not found at the beginning or the end of a block device. Support of
this feature is needed by Tegra-based devices that have TegraPT and GPT
placed in inaccessible by kernel locations. The GPT entry duplicates
TegraPT partitions.
Secondly, some Tegra-based devices have bootloader that enforces the GPT
scanning of the backup/alternative GPT entry by providing "gpt" cmdline
option to the kernel, but doesn't provide the "gpt_sector" option.
In this case GPT entry resides at a special offset from the end of eMMC
storage. It is a common situation for older bootloader versions.
The offset is calculated as a total number of eMMC sectors minus number of
eMMC boot sectors minus 1. This equation is explicitly defined and used
by the downstream Tegra kernels for locating GPT entry.
Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
---
block/partitions/check.h | 1 +
block/partitions/core.c | 1 +
block/partitions/efi.c | 9 +++++++
block/partitions/tegra.c | 57 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 68 insertions(+)
diff --git a/block/partitions/check.h b/block/partitions/check.h
index 55acf6340e5b..1ce445d1c7f0 100644
--- a/block/partitions/check.h
+++ b/block/partitions/check.h
@@ -68,5 +68,6 @@ int osf_partition(struct parsed_partitions *state);
int sgi_partition(struct parsed_partitions *state);
int sun_partition(struct parsed_partitions *state);
int sysv68_partition(struct parsed_partitions *state);
+int tegra_partition_forced_gpt(struct parsed_partitions *state);
int tegra_partition(struct parsed_partitions *state);
int ultrix_partition(struct parsed_partitions *state);
diff --git a/block/partitions/core.c b/block/partitions/core.c
index 0b4720372f07..1931647d9742 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -83,6 +83,7 @@ static int (*check_part[])(struct parsed_partitions *) = {
sysv68_partition,
#endif
#ifdef CONFIG_TEGRA_PARTITION
+ tegra_partition_forced_gpt,
tegra_partition,
#endif
NULL
diff --git a/block/partitions/efi.c b/block/partitions/efi.c
index f0229e7a6894..f8036fd55501 100644
--- a/block/partitions/efi.c
+++ b/block/partitions/efi.c
@@ -101,6 +101,15 @@ static int force_gpt;
static int __init
force_gpt_fn(char *str)
{
+ /*
+ * This check allows to properly parse cmdline variants like
+ * "gpt gpt_sector=<sector>" and "gpt_sector=<sector> gpt" since
+ * "gpt" overlaps with the "gpt_sector=", see tegra_gpt_sector_fn().
+ * The argument should be absent for a boolean cmdline option.
+ */
+ if (strlen(str))
+ return 0;
+
force_gpt = 1;
return 1;
}
diff --git a/block/partitions/tegra.c b/block/partitions/tegra.c
index d3a00ade145a..831dedb9a11c 100644
--- a/block/partitions/tegra.c
+++ b/block/partitions/tegra.c
@@ -565,3 +565,60 @@ int tegra_partition(struct parsed_partitions *state)
return ret;
}
+
+/*
+ * This allows a kernel command line option 'gpt_sector=<sector>' to
+ * enable GPT header lookup at a non-standard location. This option
+ * is provided to kernel by NVIDIA's proprietary bootloader.
+ */
+static sector_t tegra_gpt_sector;
+static int __init tegra_gpt_sector_fn(char *str)
+{
+ WARN_ON(kstrtoull(str, 10, &tegra_gpt_sector) < 0);
+ return 1;
+}
+__setup("gpt_sector=", tegra_gpt_sector_fn);
+
+int tegra_partition_forced_gpt(struct parsed_partitions *state)
+{
+ int ret = 0;
+
+#ifdef CONFIG_EFI_PARTITION
+ struct tegra_partition_table_parser ptp = {};
+
+ if (!soc_is_tegra() || !tegra_boot_sdmmc)
+ return 0;
+
+ ptp.state = state;
+
+ ptp.boot_offset = tegra_partition_table_emmc_boot_offset(&ptp);
+ if (ptp.boot_offset < 0)
+ return 0;
+
+ /*
+ * Some Tegra devices do not use gpt_sector=<sector> kernel command
+ * line option. In this case these devices usually have a GPT entry
+ * at the end of the block device and the GPT entry address is
+ * calculated this way for eMMC:
+ *
+ * gpt_sector = ext_csd.sectors_num - ext_csd.boot_sectors_num - 1
+ *
+ * This algorithm is defined and used by NVIDIA in the downstream
+ * kernel of those devices.
+ *
+ * Please note that bootloader supplies the "gpt" cmdline option
+ * which enforces the GPT scanning, meaning that the scanning will
+ * be a NO-OP on devices that do not use GPT.
+ */
+ if (tegra_gpt_sector) {
+ state->force_gpt_sector = tegra_gpt_sector;
+ } else {
+ state->force_gpt_sector = get_capacity(state->bdev->bd_disk);
+ state->force_gpt_sector -= ptp.boot_offset + 1;
+ }
+
+ ret = efi_partition(state);
+ state->force_gpt_sector = 0;
+#endif
+ return ret;
+}
--
2.26.0
