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From:   Michael Walle <michael@walle.cc>
To:     linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Tudor Ambarus <tudor.ambarus@microchip.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        Michael Walle <michael@walle.cc>
Subject: [PATCH v3] mtd: spi-nor: keep lock bits if they are non-volatile
Date:   Fri, 27 Mar 2020 16:59:39 +0100
Message-Id: <20200327155939.13153-1-michael@walle.cc>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Traditionally, linux unlocks the whole flash because there are legacy
devices which has the write protections bits set by default at startup.
If you actually want to use the flash protection bits, eg. because there
is a read-only part for a bootloader, this automatic unlocking is
harmful. If there is no hardware write protection in place (usually
called WP#), a startup of the kernel just discards this protection.

I've gone through the datasheets of all the flashes (except the Intel
ones where I could not find any datasheet nor reference) which supports
the unlocking feature and looked how the sector protection was
implemented. The currently supported flashes can be divided into the
following two categories:
 (1) block protection bits are non-volatile. Thus they keep their values
     at reset and power-cycle
 (2) flashes where these bits are volatile. After reset or power-cycle,
     the whole memory array is protected.
     (a) some devices needs a special "Global Unprotect" command, eg.
         the Atmel AT25DF041A.
     (b) some devices require to clear the BPn bits in the status
         register.

Due to the reasons above, we do not want to clear the bits for flashes
which belong to category (1). Fortunately for us, the flashes in (2a)
and (2b) are compatible with each other in a sense that the "Global
Unprotect" command will clear the block protection bits in all the (2b)
flashes.

This patch adds a new flag to indicate the case (2). Only if we have
such a flash we perform a "Global Unprotect". To be backwards compatible
it also introduces a kernel configuration option which is by default
set to "Disable write protection on any flashes". Hopefully, this will
clean up "unlock the entire flash for legacy devices" once and for all.

For reference here are the actually commits which introduced the legacy
behaviour (and extended the behaviour to other chip manufacturers):

commit f80e521c916cb ("mtd: m25p80: add support for the Intel/Numonyx {16,32,64}0S33B SPI flash chips")
commit ea60658a08f8f ("mtd: m25p80: disable SST software protection bits by default")
commit 7228982442365 ("[MTD] m25p80: fix bug - ATmel spi flash fails to be copied to")

Actually, this might also fix handling of the Atmel AT25DF flashes,
because the original commit 7228982442365 ("[MTD] m25p80: fix bug -
ATmel spi flash fails to be copied to") was writing a 0 to the status
register, which is a "Global Unprotect". This might not be the case in
the current code which only handles the block protection bits BP2, BP1
and BP0. Thus, it depends on the current contents of the status register
if this unlock actually corresponds to a "Global Unprotect" command. In
the worst case, the current code might leave the AT25DF flashes in a
write protected state.

The commit 191f5c2ed4b6f ("mtd: spi-nor: use 16-bit WRR command when QE
is set on spansion flashes") changed that behaviour by just clearing BP2
to BP0 instead of writing a 0 to the status register.

Further, the commit 3e0930f109e76 ("mtd: spi-nor: Rework the disabling of
block write protection") expanded the unlock_all() feature to ANY flash
which supports locking.

Signed-off-by: Michael Walle <michael@walle.cc>
---
changes since v2:
 - add Kconfig option to be able to retain legacy behaviour
 - rebased the patch due to the spi-nor rewrite
 - dropped the Fixes: tag, it doens't make sense after the spi-nor rewrite
 - mention commit 3e0930f109e76 which further modified the unlock
   behaviour.

changes since v1:
 - completely rewrote patch, the first version used a device tree flag

 drivers/mtd/spi-nor/Kconfig | 35 +++++++++++++++++++++++++++++
 drivers/mtd/spi-nor/atmel.c | 24 +++++++++++++-------
 drivers/mtd/spi-nor/core.c  | 44 ++++++++++++++++++++++++++++---------
 drivers/mtd/spi-nor/core.h  |  6 +++++
 drivers/mtd/spi-nor/esmt.c  |  6 ++---
 drivers/mtd/spi-nor/intel.c |  6 ++---
 drivers/mtd/spi-nor/sst.c   | 21 +++++++++---------
 include/linux/mtd/spi-nor.h |  6 +++++
 8 files changed, 114 insertions(+), 34 deletions(-)

diff --git a/drivers/mtd/spi-nor/Kconfig b/drivers/mtd/spi-nor/Kconfig
index 6e816eafb312..647de17c81e2 100644
--- a/drivers/mtd/spi-nor/Kconfig
+++ b/drivers/mtd/spi-nor/Kconfig
@@ -24,6 +24,41 @@ config MTD_SPI_NOR_USE_4K_SECTORS
 	  Please note that some tools/drivers/filesystems may not work with
 	  4096 B erase size (e.g. UBIFS requires 15 KiB as a minimum).
 
+choice
+	prompt "Write protection at boot"
+	default MTD_SPI_NOR_WP_DISABLE
+
+config MTD_SPI_NOR_WP_DISABLE
+	bool "Disable WP on any flashes (legacy behaviour)"
+	help
+	  This option disables the write protection on any SPI flashes at
+	  boot-up.
+
+	  Don't use this if you intent to use the write protection of your
+	  SPI flash. This is only to keep backwards compatibility.
+
+config MTD_SPI_NOR_WP_DISABLE_ON_VOLATILE
+	bool "Disable WP on flashes w/ volatile protection bits"
+	help
+	  Some SPI flashes have volatile block protection bits, ie. after a
+	  power-up or a reset the flash is write protected by default.
+
+	  This option disables the write protection for these kind of flashes
+	  while keeping it enabled for any other SPI flashes which have
+	  non-volatile block protection bits.
+
+	  If you are unsure, select this option.
+
+config MTD_SPI_NOR_WP_KEEP
+	bool "Keep write protection as is"
+	help
+	  If you select this option the write protection of any SPI flashes
+	  will not be changed. If your flash is write protected or will be
+	  automatically write protected after power-up you have to manually
+	  unlock it before you are able to write to it.
+
+endchoice
+
 source "drivers/mtd/spi-nor/controllers/Kconfig"
 
 endif # MTD_SPI_NOR
diff --git a/drivers/mtd/spi-nor/atmel.c b/drivers/mtd/spi-nor/atmel.c
index 3f5f21a473a6..bad6736f5a47 100644
--- a/drivers/mtd/spi-nor/atmel.c
+++ b/drivers/mtd/spi-nor/atmel.c
@@ -13,18 +13,26 @@ static const struct flash_info atmel_parts[] = {
 	{ "at25fs010",  INFO(0x1f6601, 0, 32 * 1024,   4, SECT_4K) },
 	{ "at25fs040",  INFO(0x1f6604, 0, 64 * 1024,   8, SECT_4K) },
 
-	{ "at25df041a", INFO(0x1f4401, 0, 64 * 1024,   8, SECT_4K) },
-	{ "at25df321",  INFO(0x1f4700, 0, 64 * 1024,  64, SECT_4K) },
-	{ "at25df321a", INFO(0x1f4701, 0, 64 * 1024,  64, SECT_4K) },
-	{ "at25df641",  INFO(0x1f4800, 0, 64 * 1024, 128, SECT_4K) },
+	{ "at25df041a", INFO(0x1f4401, 0, 64 * 1024,   8,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at25df321",  INFO(0x1f4700, 0, 64 * 1024,  64,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at25df321a", INFO(0x1f4701, 0, 64 * 1024,  64,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at25df641",  INFO(0x1f4800, 0, 64 * 1024, 128,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
 
 	{ "at25sl321",	INFO(0x1f4216, 0, 64 * 1024, 64,
 			     SECT_4K | SPI_NOR_DUAL_READ | SPI_NOR_QUAD_READ) },
 
-	{ "at26f004",   INFO(0x1f0400, 0, 64 * 1024,  8, SECT_4K) },
-	{ "at26df081a", INFO(0x1f4501, 0, 64 * 1024, 16, SECT_4K) },
-	{ "at26df161a", INFO(0x1f4601, 0, 64 * 1024, 32, SECT_4K) },
-	{ "at26df321",  INFO(0x1f4700, 0, 64 * 1024, 64, SECT_4K) },
+	{ "at26f004",   INFO(0x1f0400, 0, 64 * 1024,  8,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at26df081a", INFO(0x1f4501, 0, 64 * 1024, 16,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at26df161a", INFO(0x1f4601, 0, 64 * 1024, 32,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
+	{ "at26df321",  INFO(0x1f4700, 0, 64 * 1024, 64,
+			     SECT_4K | SPI_NOR_UNPROTECT) },
 
 	{ "at45db081d", INFO(0x1f2500, 0, 64 * 1024, 16, SECT_4K) },
 };
diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index cc68ea84318e..fd1c36d70a13 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2916,20 +2916,38 @@ static int spi_nor_quad_enable(struct spi_nor *nor)
 }
 
 /**
- * spi_nor_unlock_all() - Unlocks the entire flash memory array.
+ * spi_nor_global_unprotect() - Perform a global unprotect of the memory area.
  * @nor:	pointer to a 'struct spi_nor'.
  *
  * Some SPI NOR flashes are write protected by default after a power-on reset
  * cycle, in order to avoid inadvertent writes during power-up. Backward
  * compatibility imposes to unlock the entire flash memory array at power-up
- * by default.
+ * by default. Do it only for flashes where the block protection bits
+ * are volatile, this is indicated by SNOR_F_NEED_UNPROTECT.
+ *
+ * We cannot use spi_nor_unlock(nor->params.size) here because there are
+ * legacy devices (eg. AT25DF041A) which need a "global unprotect" command.
+ * This is done by writing 0b0x0000xx to the status register. This will also
+ * work for all other flashes which have these bits mapped to BP0 to BP3.
+ * The top most bit is ususally some kind of lock bit for the block
+ * protection bits.
  */
-static int spi_nor_unlock_all(struct spi_nor *nor)
+static int spi_nor_global_unprotect(struct spi_nor *nor)
 {
-	if (nor->flags & SNOR_F_HAS_LOCK)
-		return spi_nor_unlock(&nor->mtd, 0, nor->params->size);
+	int ret;
 
-	return 0;
+	dev_dbg(nor->dev, "unprotecting entire flash\n");
+	ret = spi_nor_read_sr(nor, nor->bouncebuf);
+	if (ret)
+		return ret;
+
+	nor->bouncebuf[0] &= ~SR_GLOBAL_UNPROTECT_MASK;
+
+	/*
+	 * Don't use spi_nor_write_sr1_and_check() because writing the status
+	 * register might fail if the flash is hardware write protected.
+	 */
+	return spi_nor_write_sr(nor, nor->bouncebuf, 1);
 }
 
 static int spi_nor_init(struct spi_nor *nor)
@@ -2942,10 +2960,14 @@ static int spi_nor_init(struct spi_nor *nor)
 		return err;
 	}
 
-	err = spi_nor_unlock_all(nor);
-	if (err) {
-		dev_dbg(nor->dev, "Failed to unlock the entire flash memory array\n");
-		return err;
+	if (IS_ENABLED(CONFIG_MTD_SPI_NOR_WP_DISABLE) ||
+	    (IS_ENABLED(CONFIG_MTD_SPI_NOR_WP_DISABLE_ON_VOLATILE) &&
+	     nor->flags & SNOR_F_NEED_UNPROTECT)) {
+		err = spi_nor_global_unprotect(nor);
+		if (err) {
+			dev_err(nor->dev, "global unprotect failed\n");
+			return err;
+		}
 	}
 
 	if (nor->addr_width == 4 && !(nor->flags & SNOR_F_4B_OPCODES)) {
@@ -3170,6 +3192,8 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 		nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
 	if (info->flags & USE_CLSR)
 		nor->flags |= SNOR_F_USE_CLSR;
+	if (info->flags & SPI_NOR_UNPROTECT)
+		nor->flags |= SNOR_F_NEED_UNPROTECT;
 
 	if (info->flags & SPI_NOR_4BIT_BP) {
 		nor->flags |= SNOR_F_HAS_4BIT_BP;
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index 6f2f6b27173f..9a33c023717f 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -26,6 +26,7 @@ enum spi_nor_option_flags {
 	SNOR_F_HAS_SR_TB_BIT6	= BIT(11),
 	SNOR_F_HAS_4BIT_BP      = BIT(12),
 	SNOR_F_HAS_SR_BP3_BIT6  = BIT(13),
+	SNOR_F_NEED_UNPROTECT	= BIT(14),
 };
 
 struct spi_nor_read_command {
@@ -311,6 +312,11 @@ struct flash_info {
 					 * BP3 is bit 6 of status register.
 					 * Must be used with SPI_NOR_4BIT_BP.
 					 */
+#define SPI_NOR_UNPROTECT	BIT(19)	/*
+					 * Flash is write-protected after
+					 * power-up and needs a global
+					 * unprotect.
+					 */
 
 	/* Part specific fixup hooks. */
 	const struct spi_nor_fixups *fixups;
diff --git a/drivers/mtd/spi-nor/esmt.c b/drivers/mtd/spi-nor/esmt.c
index c93170008118..f4b603b418ae 100644
--- a/drivers/mtd/spi-nor/esmt.c
+++ b/drivers/mtd/spi-nor/esmt.c
@@ -11,11 +11,11 @@
 static const struct flash_info esmt_parts[] = {
 	/* ESMT */
 	{ "f25l32pa", INFO(0x8c2016, 0, 64 * 1024, 64,
-			   SECT_4K | SPI_NOR_HAS_LOCK) },
+			   SECT_4K | SPI_NOR_HAS_LOCK | SPI_NOR_UNPROTECT) },
 	{ "f25l32qa", INFO(0x8c4116, 0, 64 * 1024, 64,
-			   SECT_4K | SPI_NOR_HAS_LOCK) },
+			   SECT_4K | SPI_NOR_HAS_LOCK | SPI_NOR_UNPROTECT) },
 	{ "f25l64qa", INFO(0x8c4117, 0, 64 * 1024, 128,
-			   SECT_4K | SPI_NOR_HAS_LOCK) },
+			   SECT_4K | SPI_NOR_HAS_LOCK | SPI_NOR_UNPROTECT) },
 };
 
 const struct spi_nor_manufacturer spi_nor_esmt = {
diff --git a/drivers/mtd/spi-nor/intel.c b/drivers/mtd/spi-nor/intel.c
index d8196f101368..001cafeb1b12 100644
--- a/drivers/mtd/spi-nor/intel.c
+++ b/drivers/mtd/spi-nor/intel.c
@@ -10,9 +10,9 @@
 
 static const struct flash_info intel_parts[] = {
 	/* Intel/Numonyx -- xxxs33b */
-	{ "160s33b",  INFO(0x898911, 0, 64 * 1024,  32, 0) },
-	{ "320s33b",  INFO(0x898912, 0, 64 * 1024,  64, 0) },
-	{ "640s33b",  INFO(0x898913, 0, 64 * 1024, 128, 0) },
+	{ "160s33b",  INFO(0x898911, 0, 64 * 1024,  32, SPI_NOR_UNPROTECT) },
+	{ "320s33b",  INFO(0x898912, 0, 64 * 1024,  64, SPI_NOR_UNPROTECT) },
+	{ "640s33b",  INFO(0x898913, 0, 64 * 1024, 128, SPI_NOR_UNPROTECT) },
 };
 
 static void intel_default_init(struct spi_nor *nor)
diff --git a/drivers/mtd/spi-nor/sst.c b/drivers/mtd/spi-nor/sst.c
index e0af6d25d573..5e0412caf40d 100644
--- a/drivers/mtd/spi-nor/sst.c
+++ b/drivers/mtd/spi-nor/sst.c
@@ -11,26 +11,27 @@
 static const struct flash_info sst_parts[] = {
 	/* SST -- large erase sizes are "overlays", "sectors" are 4K */
 	{ "sst25vf040b", INFO(0xbf258d, 0, 64 * 1024,  8,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25vf080b", INFO(0xbf258e, 0, 64 * 1024, 16,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25vf016b", INFO(0xbf2541, 0, 64 * 1024, 32,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25vf032b", INFO(0xbf254a, 0, 64 * 1024, 64,
-			      SECT_4K | SST_WRITE) },
-	{ "sst25vf064c", INFO(0xbf254b, 0, 64 * 1024, 128, SECT_4K) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
+	{ "sst25vf064c", INFO(0xbf254b, 0, 64 * 1024, 128,
+			      SECT_4K | SPI_NOR_UNPROTECT) },
 	{ "sst25wf512",  INFO(0xbf2501, 0, 64 * 1024,  1,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25wf010",  INFO(0xbf2502, 0, 64 * 1024,  2,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25wf020",  INFO(0xbf2503, 0, 64 * 1024,  4,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25wf020a", INFO(0x621612, 0, 64 * 1024,  4, SECT_4K) },
 	{ "sst25wf040b", INFO(0x621613, 0, 64 * 1024,  8, SECT_4K) },
 	{ "sst25wf040",  INFO(0xbf2504, 0, 64 * 1024,  8,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst25wf080",  INFO(0xbf2505, 0, 64 * 1024, 16,
-			      SECT_4K | SST_WRITE) },
+			      SECT_4K | SST_WRITE | SPI_NOR_UNPROTECT) },
 	{ "sst26wf016b", INFO(0xbf2651, 0, 64 * 1024, 32,
 			      SECT_4K | SPI_NOR_DUAL_READ |
 			      SPI_NOR_QUAD_READ) },
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index 1e2af0ec1f03..f0a27cf8536b 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -124,6 +124,12 @@
 
 #define SR_BP_SHIFT		2
 
+/*
+ * Global unprotect is performed by writing the 0b0x0000xx to the status
+ * register.
+ */
+#define SR_GLOBAL_UNPROTECT_MASK 0xbc
+
 /* Enhanced Volatile Configuration Register bits */
 #define EVCR_QUAD_EN_MICRON	BIT(7)	/* Micron Quad I/O */
 
-- 
2.20.1