[PATCH v2 2/2] mtd: nand: omap: Synchronize access to the ECC engine

[Rostislav Lisovy <lisovy@gmail.com>]

The AM335x Technical Reference Manual (spruh73j.pdf) says
"Because the ECC engine includes only one accumulation context,
it can be allocated to only one chip-select at a time ... "
(7.1.3.3.12.3). Since the commit 97a288ba2cfa ("ARM: omap2+:
gpmc-nand: Use dynamic platform_device_alloc()") gpmc-nand
driver supports multiple NAND flash devices connected to
the single controller. Use mutexes to restrict access
to the ECC engine for single read/write operation at a time.

Tested with custom AM335x board using 2x NAND flash chips.

Signed-off-by: Rostislav Lisovy <lisovy@merica.cz>
---
Changes since v1:
* Since not all the read/write operations are performed by the
  omap_read(write)_page_bch() functions use the locks directly on
  those places that configure the ECC engine (take the lock) and
  read the result from the ECC engine (release the lock).
  This approach should cover read/write operations with all
  possible ECC modes. (Roger Quadros)


 drivers/mtd/nand/omap2.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index f0dcdb6..898cb44 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -24,6 +24,7 @@
 #include <linux/slab.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/mutex.h>
 
 #include <linux/mtd/nand_bch.h>
 #include <linux/platform_data/elm.h>
@@ -144,6 +145,12 @@ static u_char bch8_vector[] = {0xf3, 0xdb, 0x14, 0x16, 0x8b, 0xd2, 0xbe, 0xcc,
 	0xac, 0x6b, 0xff, 0x99, 0x7b};
 static u_char bch4_vector[] = {0x00, 0x6b, 0x31, 0xdd, 0x41, 0xbc, 0x10};
 
+/*
+ * Because the ECC engine includes only one accumulation context,
+ * it can be allocated to only one chip-select at a time
+ */
+static DEFINE_MUTEX(omap_eccengine_lock);
+
 struct omap_nand_info {
 	struct nand_hw_control		controller;
 	struct omap_nand_platform_data	*pdata;
@@ -926,10 +933,13 @@ static int omap_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
 	struct omap_nand_info *info = container_of(mtd, struct omap_nand_info,
 							mtd);
 	u32 val;
+	int ret = 0;
 
 	val = readl(info->reg.gpmc_ecc_config);
-	if (((val >> ECC_CONFIG_CS_SHIFT) & CS_MASK) != info->gpmc_cs)
-		return -EINVAL;
+	if (((val >> ECC_CONFIG_CS_SHIFT) & CS_MASK) != info->gpmc_cs) {
+		ret = -EINVAL;
+		goto leave;
+	}
 
 	/* read ecc result */
 	val = readl(info->reg.gpmc_ecc1_result);
@@ -938,7 +948,10 @@ static int omap_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
 	/* P2048o, P1024o, P512o, P256o, P2048e, P1024e, P512e, P256e */
 	*ecc_code++ = ((val >> 8) & 0x0f) | ((val >> 20) & 0xf0);
 
-	return 0;
+leave:
+	/* Release the ECC engine */
+	mutex_unlock(&omap_eccengine_lock);
+	return ret;
 }
 
 /**
@@ -954,6 +967,9 @@ static void omap_enable_hwecc(struct mtd_info *mtd, int mode)
 	unsigned int dev_width = (chip->options & NAND_BUSWIDTH_16) ? 1 : 0;
 	u32 val;
 
+	/* ECC Engine is shared among multiple NAND devices */
+	mutex_lock(&omap_eccengine_lock);
+
 	/* clear ecc and enable bits */
 	val = ECCCLEAR | ECC1;
 	writel(val, info->reg.gpmc_ecc_control);
@@ -1132,6 +1148,9 @@ static void __maybe_unused omap_enable_hwecc_bch(struct mtd_info *mtd, int mode)
 		return;
 	}
 
+	/* ECC Engine is shared among multiple NAND devices */
+	mutex_lock(&omap_eccengine_lock);
+
 	writel(ECC1, info->reg.gpmc_ecc_control);
 
 	/* Configure ecc size for BCH */
@@ -1252,6 +1271,7 @@ static int __maybe_unused omap_calculate_ecc_bch(struct mtd_info *mtd,
 			ecc_code[25] = ((val >>  0) & 0xFF);
 			break;
 		default:
+			mutex_unlock(&omap_eccengine_lock);
 			return -EINVAL;
 		}
 
@@ -1280,12 +1300,14 @@ static int __maybe_unused omap_calculate_ecc_bch(struct mtd_info *mtd,
 		case OMAP_ECC_BCH16_CODE_HW:
 			break;
 		default:
+			mutex_unlock(&omap_eccengine_lock);
 			return -EINVAL;
 		}
 
 	ecc_calc += eccbytes;
 	}
 
+	mutex_unlock(&omap_eccengine_lock);
 	return 0;
 }
 
-- 
1.9.1