Commit 62593cf4 authored by Brian Norris's avatar Brian Norris
Browse files

mtd: spi-nor: refactor block protection functions 



This code was a bit sloppy, would produce a lot of copy-and-paste, and
did not always provide a sensible interface:

 * It didn't validate the length for LOCK and the offset for UNLOCK, so
   we were essentially discarding half of the user-supplied data and
   assuming what they wanted to lock/unlock
 * It didn't do very good error checking
 * It didn't make use of the fact that this operation works on
   power-of-two dimensions

So, rewrite this to do proper bit arithmetic rather than a bunch of
hard-coded condition tables. Now we have:

 * More comments on how this was derived
 * Notes on what is (and isn't) supported
 * A more exendible function, so we could add support for other
   protection ranges
 * More accurate locking - e.g., suppose the top quadrant is locked (75%
   to 100%); then in the following cases, case (a) will succeed but (b)
   will not (return -EINVAL):
     (a) user requests lock 3rd quadrant (50% to 75%)
     (b) user requests lock 3rd quadrant, minus a few blocks (e.g., 50%
         to 73%)
   Case (b) *should* fail, since we'd have to lock blocks that weren't
   requested. But the old implementation didn't know the difference and
   would lock the entire second half (50% to 100%)

This refactoring work will also help enable the addition of
mtd_is_locked() support and potentially the support of bottom boot
protection (TB=1).

Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
parent f8900258

drivers/mtd/spi-nor/spi-nor.c

+126 −45
Original line number Diff line number Diff line
@@ -400,72 +400,153 @@ erase_err: 
	return ret;

}



static void stm_get_locked_range(struct spi_nor *nor, u8 sr, loff_t *ofs,

				 uint64_t *len)

{

	struct mtd_info *mtd = &nor->mtd;

	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;

	int shift = ffs(mask) - 1;

	int pow;



	if (!(sr & mask)) {

		/* No protection */

		*ofs = 0;

		*len = 0;

	} else {

		pow = ((sr & mask) ^ mask) >> shift;

		*len = mtd->size >> pow;

		*ofs = mtd->size - *len;

	}

}



/*

 * Return 1 if the entire region is locked, 0 otherwise

 */

static int stm_is_locked_sr(struct spi_nor *nor, loff_t ofs, uint64_t len,

			    u8 sr)

{

	loff_t lock_offs;

	uint64_t lock_len;



	stm_get_locked_range(nor, sr, &lock_offs, &lock_len);



	return (ofs + len <= lock_offs + lock_len) && (ofs >= lock_offs);

}



/*

 * Lock a region of the flash. Compatible with ST Micro and similar flash.

 * Supports only the block protection bits BP{0,1,2} in the status register

 * (SR). Does not support these features found in newer SR bitfields:

 *   - TB: top/bottom protect - only handle TB=0 (top protect)

 *   - SEC: sector/block protect - only handle SEC=0 (block protect)

 *   - CMP: complement protect - only support CMP=0 (range is not complemented)

 *

 * Sample table portion for 8MB flash (Winbond w25q64fw):

 *

 *   SEC  |  TB   |  BP2  |  BP1  |  BP0  |  Prot Length  | Protected Portion

 *  --------------------------------------------------------------------------

 *    X   |   X   |   0   |   0   |   0   |  NONE         | NONE

 *    0   |   0   |   0   |   0   |   1   |  128 KB       | Upper 1/64

 *    0   |   0   |   0   |   1   |   0   |  256 KB       | Upper 1/32

 *    0   |   0   |   0   |   1   |   1   |  512 KB       | Upper 1/16

 *    0   |   0   |   1   |   0   |   0   |  1 MB         | Upper 1/8

 *    0   |   0   |   1   |   0   |   1   |  2 MB         | Upper 1/4

 *    0   |   0   |   1   |   1   |   0   |  4 MB         | Upper 1/2

 *    X   |   X   |   1   |   1   |   1   |  8 MB         | ALL

 *

 * Returns negative on errors, 0 on success.

 */

static int stm_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)

{

	struct mtd_info *mtd = &nor->mtd;

	uint32_t offset = ofs;

	uint8_t status_old, status_new;

	int ret = 0;

	u8 status_old, status_new;

	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;

	u8 shift = ffs(mask) - 1, pow, val;



	status_old = read_sr(nor);



	if (offset < mtd->size - (mtd->size / 2))

		status_new = status_old | SR_BP2 | SR_BP1 | SR_BP0;

	else if (offset < mtd->size - (mtd->size / 4))

		status_new = (status_old & ~SR_BP0) | SR_BP2 | SR_BP1;

	else if (offset < mtd->size - (mtd->size / 8))

		status_new = (status_old & ~SR_BP1) | SR_BP2 | SR_BP0;

	else if (offset < mtd->size - (mtd->size / 16))

		status_new = (status_old & ~(SR_BP0 | SR_BP1)) | SR_BP2;

	else if (offset < mtd->size - (mtd->size / 32))

		status_new = (status_old & ~SR_BP2) | SR_BP1 | SR_BP0;

	else if (offset < mtd->size - (mtd->size / 64))

		status_new = (status_old & ~(SR_BP2 | SR_BP0)) | SR_BP1;

	else

		status_new = (status_old & ~(SR_BP2 | SR_BP1)) | SR_BP0;

	/* SPI NOR always locks to the end */

	if (ofs + len != mtd->size) {

		/* Does combined region extend to end? */

		if (!stm_is_locked_sr(nor, ofs + len, mtd->size - ofs - len,

				      status_old))

			return -EINVAL;

		len = mtd->size - ofs;

	}



	/*

	 * Need smallest pow such that:

	 *

	 *   1 / (2^pow) <= (len / size)

	 *

	 * so (assuming power-of-2 size) we do:

	 *

	 *   pow = ceil(log2(size / len)) = log2(size) - floor(log2(len))

	 */

	pow = ilog2(mtd->size) - ilog2(len);

	val = mask - (pow << shift);

	if (val & ~mask)

		return -EINVAL;

	/* Don't "lock" with no region! */

	if (!(val & mask))

		return -EINVAL;



	status_new = (status_old & ~mask) | val;



	/* Only modify protection if it will not unlock other areas */

	if ((status_new & (SR_BP2 | SR_BP1 | SR_BP0)) >

				(status_old & (SR_BP2 | SR_BP1 | SR_BP0))) {

		write_enable(nor);

		ret = write_sr(nor, status_new);

	}

	if ((status_new & mask) <= (status_old & mask))

		return -EINVAL;



	return ret;

	write_enable(nor);

	return write_sr(nor, status_new);

}



/*

 * Unlock a region of the flash. See stm_lock() for more info

 *

 * Returns negative on errors, 0 on success.

 */

static int stm_unlock(struct spi_nor *nor, loff_t ofs, uint64_t len)

{

	struct mtd_info *mtd = &nor->mtd;

	uint32_t offset = ofs;

	uint8_t status_old, status_new;

	int ret = 0;

	u8 mask = SR_BP2 | SR_BP1 | SR_BP0;

	u8 shift = ffs(mask) - 1, pow, val;



	status_old = read_sr(nor);



	if (offset+len > mtd->size - (mtd->size / 64))

		status_new = status_old & ~(SR_BP2 | SR_BP1 | SR_BP0);

	else if (offset+len > mtd->size - (mtd->size / 32))

		status_new = (status_old & ~(SR_BP2 | SR_BP1)) | SR_BP0;

	else if (offset+len > mtd->size - (mtd->size / 16))

		status_new = (status_old & ~(SR_BP2 | SR_BP0)) | SR_BP1;

	else if (offset+len > mtd->size - (mtd->size / 8))

		status_new = (status_old & ~SR_BP2) | SR_BP1 | SR_BP0;

	else if (offset+len > mtd->size - (mtd->size / 4))

		status_new = (status_old & ~(SR_BP0 | SR_BP1)) | SR_BP2;

	else if (offset+len > mtd->size - (mtd->size / 2))

		status_new = (status_old & ~SR_BP1) | SR_BP2 | SR_BP0;

	else

		status_new = (status_old & ~SR_BP0) | SR_BP2 | SR_BP1;

	/* Cannot unlock; would unlock larger region than requested */

	if (stm_is_locked_sr(nor, status_old, ofs - mtd->erasesize,

			     mtd->erasesize))

		return -EINVAL;



	/* Only modify protection if it will not lock other areas */

	if ((status_new & (SR_BP2 | SR_BP1 | SR_BP0)) <

				(status_old & (SR_BP2 | SR_BP1 | SR_BP0))) {

		write_enable(nor);

		ret = write_sr(nor, status_new);

	/*

	 * Need largest pow such that:

	 *

	 *   1 / (2^pow) >= (len / size)

	 *

	 * so (assuming power-of-2 size) we do:

	 *

	 *   pow = floor(log2(size / len)) = log2(size) - ceil(log2(len))

	 */

	pow = ilog2(mtd->size) - order_base_2(mtd->size - (ofs + len));

	if (ofs + len == mtd->size) {

		val = 0; /* fully unlocked */

	} else {

		val = mask - (pow << shift);

		/* Some power-of-two sizes are not supported */

		if (val & ~mask)

			return -EINVAL;

	}



	return ret;

	status_new = (status_old & ~mask) | val;



	/* Only modify protection if it will not lock other areas */

	if ((status_new & mask) >= (status_old & mask))

		return -EINVAL;



	write_enable(nor);

	return write_sr(nor, status_new);

}



static int spi_nor_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)

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