mmc: core: Add wp_grp_size sysfs node

The eMMC card can be set into write-protected mode to prevent data from
being accidentally modified or deleted. Wp_grp_size (Write Protect Group
Size) refers to an attribute of the eMMC card, used to manage write
protection and is the CSD register [36:32] of the eMMC device. Wp_grp_size
(Write Protect Group Size) indicates how many eMMC blocks are contained in
each write protection group on the eMMC card.

To allow userspace easy access of the CSD register bits, let's add sysfs
node "wp_grp_size".

Signed-off-by: Lin Gui <[e-mail]>
Signed-off-by: Bo Ye <[e-mail]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/mmc.c

···
 	mmc_init_erase(card);
 }
 
+
+static void mmc_set_wp_grp_size(struct mmc_card *card)
+{
+	if (card->ext_csd.erase_group_def & 1)
+		card->wp_grp_size = card->ext_csd.hc_erase_size *
+			card->ext_csd.raw_hc_erase_gap_size;
+	else
+		card->wp_grp_size = card->csd.erase_size *
+			(card->csd.wp_grp_size + 1);
+}
+
 /*
  * Given a 128-bit response, decode to our card CSD structure.
  */
···
 		b = UNSTUFF_BITS(resp, 37, 5);
 		csd->erase_size = (a + 1) * (b + 1);
 		csd->erase_size <<= csd->write_blkbits - 9;
+		csd->wp_grp_size = UNSTUFF_BITS(resp, 32, 5);
 	}
 
 	return 0;
···
 MMC_DEV_ATTR(date, "%02d/%04d\n", card->cid.month, card->cid.year);
 MMC_DEV_ATTR(erase_size, "%u\n", card->erase_size << 9);
 MMC_DEV_ATTR(preferred_erase_size, "%u\n", card->pref_erase << 9);
+MMC_DEV_ATTR(wp_grp_size, "%u\n", card->wp_grp_size << 9);
 MMC_DEV_ATTR(ffu_capable, "%d\n", card->ext_csd.ffu_capable);
 MMC_DEV_ATTR(hwrev, "0x%x\n", card->cid.hwrev);
 MMC_DEV_ATTR(manfid, "0x%06x\n", card->cid.manfid);
···
 	&dev_attr_date.attr,
 	&dev_attr_erase_size.attr,
 	&dev_attr_preferred_erase_size.attr,
+	&dev_attr_wp_grp_size.attr,
 	&dev_attr_fwrev.attr,
 	&dev_attr_ffu_capable.attr,
 	&dev_attr_hwrev.attr,
···
 			mmc_set_erase_size(card);
 		}
 	}
-
+	mmc_set_wp_grp_size(card);
 	/*
 	 * Ensure eMMC user default partition is enabled
 	 */

include/linux/mmc/card.h

···
 	unsigned int		r2w_factor;
 	unsigned int		max_dtr;
 	unsigned int		erase_size;		/* In sectors */
+	unsigned int		wp_grp_size;
 	unsigned int		read_blkbits;
 	unsigned int		write_blkbits;
 	unsigned int		capacity;
···
 	unsigned int		eg_boundary;	/* don't cross erase-group boundaries */
 	unsigned int		erase_arg;	/* erase / trim / discard */
  	u8			erased_byte;	/* value of erased bytes */
+	unsigned int		wp_grp_size;	/* write group size in sectors */
 
 	u32			raw_cid[4];	/* raw card CID */
 	u32			raw_csd[4];	/* raw card CSD */