partitions/efi: Support NVIDIA Tegra devices

NVIDIA Tegra consumer devices have EMMC storage that has GPT entry at a
non-standard location. Support looking up GPT entry at a special sector
to enable such devices.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>

block/partitions/Kconfig

@@ -267,3 +267,11 @@ config CMDLINE_PARTITION
 	help
 	  Say Y here if you want to read the partition table from bootargs.
 	  The format for the command line is just like mtdparts.
+
+config TEGRA_PARTITION
+	bool "NVIDIA Tegra Partition support" if PARTITION_ADVANCED
+	default y if ARCH_TEGRA
+	depends on EFI_PARTITION && MMC_BLOCK && (ARCH_TEGRA || COMPILE_TEST)
+	help
+	  Say Y here if you would like to be able to read the hard disk
+	  partition table format used by NVIDIA Tegra machines.

block/partitions/Makefile

@@ -20,3 +20,4 @@ obj-$(CONFIG_IBM_PARTITION) += ibm.o
 obj-$(CONFIG_EFI_PARTITION) += efi.o
 obj-$(CONFIG_KARMA_PARTITION) += karma.o
 obj-$(CONFIG_SYSV68_PARTITION) += sysv68.o
+obj-$(CONFIG_TEGRA_PARTITION) += tegra.o

block/partitions/check.h

@@ -22,6 +22,7 @@ struct parsed_partitions {
 	int limit;
 	bool access_beyond_eod;
 	char *pp_buf;
+	sector_t force_gpt_sector;
 };
 
 typedef struct {
@@ -67,4 +68,5 @@ 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 ultrix_partition(struct parsed_partitions *state);

block/partitions/core.c

@@ -82,6 +82,9 @@ static int (*check_part[])(struct parsed_partitions *) = {
 #endif
 #ifdef CONFIG_SYSV68_PARTITION
 	sysv68_partition,
+#endif
+#ifdef CONFIG_TEGRA_PARTITION
+	tegra_partition_forced_gpt,
 #endif
 	NULL
 };

block/partitions/efi.c

@@ -619,6 +619,15 @@ static int find_valid_gpt(struct parsed_partitions *state, gpt_header **gpt,
         if (!good_agpt && force_gpt)
                 good_agpt = is_gpt_valid(state, lastlba, &agpt, &aptes);
 
+	/*
+	 * The force_gpt_sector is used by NVIDIA Tegra partition parser in
+	 * order to convey a non-standard location of the GPT entry for lookup.
+	 * By default force_gpt_sector is set to 0 and has no effect.
+	 */
+	if (!good_agpt && force_gpt && state->force_gpt_sector)
+		good_agpt = is_gpt_valid(state, state->force_gpt_sector,
+					 &agpt, &aptes);
+
         /* The obviously unsuccessful case */
         if (!good_pgpt && !good_agpt)
                 goto fail;

block/partitions/tegra.c

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define pr_fmt(fmt) "tegra-partition: " fmt
+
+#include <linux/blkdev.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/sizes.h>
+
+#include <linux/mmc/blkdev.h>
+#include <linux/mmc/card.h>
+#include <linux/mmc/host.h>
+
+#include <soc/tegra/common.h>
+
+#include "check.h"
+
+static const struct of_device_id tegra_sdhci_match[] = {
+	{ .compatible = "nvidia,tegra20-sdhci", },
+	{ .compatible = "nvidia,tegra30-sdhci", },
+	{ .compatible = "nvidia,tegra114-sdhci", },
+	{ .compatible = "nvidia,tegra124-sdhci", },
+	{}
+};
+
+int tegra_partition_forced_gpt(struct parsed_partitions *state)
+{
+	struct gendisk *disk = state->disk;
+	struct block_device *bdev = disk->part0;
+	struct mmc_card *card = mmc_bdev_to_card(bdev);
+	int ret, boot_offset;
+
+	if (!soc_is_tegra())
+		return 0;
+
+	/* filter out unrelated and untested boot sources */
+	if (!card || card->ext_csd.rev < 3 ||
+	    !mmc_card_is_blockaddr(card) ||
+	     mmc_card_is_removable(card->host) ||
+	     bdev_logical_block_size(bdev) != SZ_512 ||
+	    !of_match_node(tegra_sdhci_match, card->host->parent->of_node)) {
+		pr_debug("%s: unexpected boot source\n", disk->disk_name);
+		return 0;
+	}
+
+	/*
+	 * eMMC storage has two special boot partitions in addition to the
+	 * main one.  NVIDIA's bootloader linearizes eMMC boot0->boot1->main
+	 * accesses, this means that the partition table addresses are shifted
+	 * by the size of boot partitions.  In accordance with the eMMC
+	 * specification, the boot partition size is calculated as follows:
+	 *
+	 *	boot partition size = 128K byte x BOOT_SIZE_MULT
+	 *
+	 * This function returns number of sectors occupied by the both boot
+	 * partitions.
+	 */
+	boot_offset = card->ext_csd.raw_boot_mult * SZ_128K /
+		      SZ_512 * MMC_NUM_BOOT_PARTITION;
+
+	/*
+	 * The fixed GPT entry address is calculated like this:
+	 *
+	 * gpt_sector = ext_csd.sectors_num - ext_csd.boot_sectors_num - 1
+	 *
+	 * This algorithm is defined by NVIDIA and used by Android devices.
+	 */
+	state->force_gpt_sector  = get_capacity(disk);
+	state->force_gpt_sector -= boot_offset + 1;
+
+	ret = efi_partition(state);
+	state->force_gpt_sector = 0;
+
+	return ret;
+}