[U-Boot] [PATCH v2] sf: bar: Clean BA24 Bank Address Register bit after read/write/erase operation

[Lukasz Majewski]

The content of Bank Address Register (BAR) is volatile. It is cleared
after power cycle or reset command (RESET F0h).

Some memories (like e.g. s25fl256s) use it to access memory larger than
0x1000000 (16 MiB).

The problem shows up when one:

1. Reads/writes/erases memory > 16 MiB
2. Calls "reset" u-boot command (which is not causing BAR to be cleared)

In the above scenario, the SoC ROM sends 0x000000 address to read SPL.
Unfortunately, the BA24 bit is still set and hence it receives content
from 0x1000000 (16 MiB) memory address.
As a result the SoC aborts and we hang. Only power cycle can take the
SoC out of this state.

How to reproduce/test:

sf probe; sf erase 0x1200000 0x800000; reset
sf probe; sf erase 0x1200000 0x800000; sf write 0x11000000 0x1200000 0x800000; reset
sf probe; sf read 0x11000000 0x1200000 0x800000; reset

Signed-off-by: Lukasz Majewski <lukma at denx.de>

---
Changes in v2:

- Rename cleanup_bar() to clean_bar()
- Rewrite in-code comments
---
 drivers/mtd/spi/spi_flash.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/mtd/spi/spi_flash.c b/drivers/mtd/spi/spi_flash.c
index 34f6888..5b3c974 100644
--- a/drivers/mtd/spi/spi_flash.c
+++ b/drivers/mtd/spi/spi_flash.c
@@ -113,6 +113,27 @@ static int write_cr(struct spi_flash *flash, u8 wc)
 #endif
 
 #ifdef CONFIG_SPI_FLASH_BAR
+/*
+ * This "cleanup" is necessary in a situation when one was accessing
+ * spi flash memory > 16 MiB by using Bank Address Register's BA24 bit.
+ *
+ * After it the BA24 bit shall be cleared to allow access to correct
+ * memory region after SW reset (by calling "reset" command).
+ *
+ * Otherwise, the BA24 bit may be left set and then after reset, the
+ * ROM would read/write/erase SPL from 16 MiB * bank_sel address.
+ */
+static int clean_bar(struct spi_flash *flash)
+{
+	u8 cmd, bank_sel = 0;
+
+	if (flash->bank_curr == 0)
+		return 0;
+	cmd = flash->bank_write_cmd;
+
+	return spi_flash_write_common(flash, &cmd, 1, &bank_sel, 1);
+}
+
 static int write_bar(struct spi_flash *flash, u32 offset)
 {
 	u8 cmd, bank_sel;
@@ -339,6 +360,10 @@ int spi_flash_cmd_erase_ops(struct spi_flash *flash, u32 offset, size_t len)
 		len -= erase_size;
 	}
 
+#ifdef CONFIG_SPI_FLASH_BAR
+	ret = clean_bar(flash);
+#endif
+
 	return ret;
 }
 
@@ -397,6 +422,10 @@ int spi_flash_cmd_write_ops(struct spi_flash *flash, u32 offset,
 		offset += chunk_len;
 	}
 
+#ifdef CONFIG_SPI_FLASH_BAR
+	ret = clean_bar(flash);
+#endif
+
 	return ret;
 }
 
@@ -500,6 +529,10 @@ int spi_flash_cmd_read_ops(struct spi_flash *flash, u32 offset,
 		data += read_len;
 	}
 
+#ifdef CONFIG_SPI_FLASH_BAR
+	ret = clean_bar(flash);
+#endif
+
 	free(cmd);
 	return ret;
 }
-- 
2.1.4