sf: Support querying write-protect

This feature was dropped from U-Boot some time ago:

   f12f96cfaf (sf: Drop spl_flash_get_sw_write_prot")

However, we do need a way to see if a flash device is write-protected,
since if it is, it may not be possible to write to do (i.e. failing to
write is expected).

I am not sure of the correct layer to implement this, so this patch is a
stab at it. If spi-flash makes sense then I will add to the 'sf' also.

Re the points mentioned in the removal commit:

    1) This kind of requirement can be achieved using existing
       flash operations and flash locking API calls instead of
       making a separate flash API.

Which uclass is this?

    2) Technically there is no real hardware user for this API to
       use in the source tree.

I do want coral (at least) to support this.

    3) Having a flash operations API for simple register read bits
       also make difficult to extend the flash operations.

This new patch only mentions write-protect being on or off, rather than
the actual mechanism.

    4) Instead of touching generic code, it is possible to have
       this functionality inside spinor operations in the form of
       flash hooks or fixups for associated flash chips.

That sounds to me like what drivers are for. But we still need some sort
of API for it to be accessible.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/mtd/spi/sf-uclass.c

@@ -31,6 +31,15 @@ int spi_flash_erase_dm(struct udevice *dev, u32 offset, size_t len)
 	return log_ret(sf_get_ops(dev)->erase(dev, offset, len));
 }
 
+int spl_flash_get_sw_write_prot(struct udevice *dev)
+{
+	struct dm_spi_flash_ops *ops = sf_get_ops(dev);
+
+	if (!ops->get_sw_write_prot)
+		return -ENOSYS;
+	return log_ret(ops->get_sw_write_prot(dev));
+}
+
 /*
  * TODO(sjg@chromium.org): This is an old-style function. We should remove
  * it when all SPI flash drivers use dm

drivers/mtd/spi/sf_internal.h

@@ -75,6 +75,10 @@ extern const struct flash_info spi_nor_ids[];
 #define JEDEC_MFR(info)	((info)->id[0])
 #define JEDEC_ID(info)		(((info)->id[1]) << 8 | ((info)->id[2]))
 
+/* Get software write-protect value (BP bits) */
+int spi_flash_cmd_get_sw_write_prot(struct spi_flash *flash);
+
+
 #if CONFIG_IS_ENABLED(SPI_FLASH_MTD)
 int spi_flash_mtd_register(struct spi_flash *flash);
 void spi_flash_mtd_unregister(void);

drivers/mtd/spi/sf_probe.c

@@ -130,6 +130,13 @@ static int spi_flash_std_erase(struct udevice *dev, u32 offset, size_t len)
 	return mtd->_erase(mtd, &instr);
 }
 
+static int spi_flash_std_get_sw_write_prot(struct udevice *dev)
+{
+	struct spi_flash *flash = dev_get_uclass_priv(dev);
+
+	return spi_flash_cmd_get_sw_write_prot(flash);
+}
+
 int spi_flash_std_probe(struct udevice *dev)
 {
 	struct spi_slave *slave = dev_get_parent_priv(dev);
@@ -153,6 +160,7 @@ static const struct dm_spi_flash_ops spi_flash_std_ops = {
 	.read = spi_flash_std_read,
 	.write = spi_flash_std_write,
 	.erase = spi_flash_std_erase,
+	.get_sw_write_prot = spi_flash_std_get_sw_write_prot,
 };
 
 static const struct udevice_id spi_flash_std_ids[] = {

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

@@ -2647,3 +2647,14 @@ int spi_nor_scan(struct spi_nor *nor)
 
 	return 0;
 }
+
+/* U-Boot specific functions, need to extend MTD to support these */
+int spi_flash_cmd_get_sw_write_prot(struct spi_nor *nor)
+{
+	int sr = read_sr(nor);
+
+	if (sr < 0)
+		return sr;
+
+	return (sr >> 2) & 7;
+}

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

@@ -809,3 +809,9 @@ int spi_nor_scan(struct spi_nor *nor)
 
 	return 0;
 }
+
+/* U-Boot specific functions, need to extend MTD to support these */
+int spi_flash_cmd_get_sw_write_prot(struct spi_nor *nor)
+{
+	return -ENOTSUPP;
+}

include/spi_flash.h

@@ -35,6 +35,19 @@ struct dm_spi_flash_ops {
 	int (*write)(struct udevice *dev, u32 offset, size_t len,
 		     const void *buf);
 	int (*erase)(struct udevice *dev, u32 offset, size_t len);
+	/**
+	 * get_sw_write_prot() - Check state of software write-protect feature
+	 *
+	 * SPI flash chips can lock a region of the flash defined by a
+	 * 'protected area'. This function checks if this protected area is
+	 * defined.
+	 *
+	 * @dev:	SPI flash device
+	 * @return 0 if no region is write-protected, 1 if a region is
+	 *	write-protected, -ENOSYS if the driver does not implement this,
+	 *	other -ve value on error
+	 */
+	int (*get_sw_write_prot)(struct udevice *dev);
 };
 
 /* Access the serial operations for a device */
@@ -76,6 +89,20 @@ int spi_flash_write_dm(struct udevice *dev, u32 offset, size_t len,
  */
 int spi_flash_erase_dm(struct udevice *dev, u32 offset, size_t len);
 
+/**
+ * spl_flash_get_sw_write_prot() - Check state of software write-protect feature
+ *
+ * SPI flash chips can lock a region of the flash defined by a
+ * 'protected area'. This function checks if this protected area is
+ * defined.
+ *
+ * @dev:	SPI flash device
+ * @return 0 if no region is write-protected, 1 if a region is
+ *	write-protected, -ENOSYS if the driver does not implement this,
+ *	other -ve value on error
+ */
+int spl_flash_get_sw_write_prot(struct udevice *dev);
+
 /**
  * spi_flash_std_probe() - Probe a SPI flash device
  *

test/dm/sf.c

@@ -21,7 +21,7 @@
 /* Simple test of sandbox SPI flash */
 static int dm_test_spi_flash(struct unit_test_state *uts)
 {
-	struct udevice *dev;
+	struct udevice *dev, *emul;
 	int full_size = 0x200000;
 	int size = 0x10000;
 	u8 *src, *dst;
@@ -51,6 +51,14 @@ static int dm_test_spi_flash(struct unit_test_state *uts)
 	ut_assertok(spi_flash_read_dm(dev, 0, size, dst));
 	ut_asserteq_mem(src, dst, size);
 
+	/* Try the write-protect stuff */
+	ut_assertok(uclass_first_device_err(UCLASS_SPI_EMUL, &emul));
+	ut_asserteq(0, spl_flash_get_sw_write_prot(dev));
+	sandbox_sf_set_block_protect(emul, 1);
+	ut_asserteq(1, spl_flash_get_sw_write_prot(dev));
+	sandbox_sf_set_block_protect(emul, 0);
+	ut_asserteq(0, spl_flash_get_sw_write_prot(dev));
+
 	/* Check mapping */
 	ut_assertok(dm_spi_get_mmap(dev, &map_base, &map_size, &offset));
 	ut_asserteq(0x1000, map_base);