[1] The gpmi uses the nand_command_lp to issue the commands to NAND chips.
It will issue a DMA operation when it handles a NAND_CMD_NONE control
command. So when we read a page(NAND_CMD_READ0) from the NAND, we may send
two DMA operations back-to-back.
If we do not serialize the two DMA operations, we will meet a bug when
1.1) we enable CONFIG_DMA_API_DEBUG, CONFIG_DMADEVICES_DEBUG,
and CONFIG_DEBUG_SG.
1.2) Use the following commands in an UART console and a SSH console:
cmd 1: while true;do dd if=/dev/mtd0 of=/dev/null;done
cmd 1: while true;do dd if=/dev/mmcblk0 of=/dev/null;done
The kernel log shows below:
-----------------------------------------------------------------
kernel BUG at lib/scatterlist.c:28!
Unable to handle kernel NULL pointer dereference at virtual address 00000000
.........................
[<80044a0c>] (__bug+0x18/0x24) from [<80249b74>] (sg_next+0x48/0x4c)
[<80249b74>] (sg_next+0x48/0x4c) from [<80255398>]
(debug_dma_unmap_sg+0x170/0x1a4)
[<80255398>] (debug_dma_unmap_sg+0x170/0x1a4) from [<8004af58>]
(dma_unmap_sg+0x14/0x6c)
[<8004af58>] (dma_unmap_sg+0x14/0x6c) from [<8027e594>]
(mxs_dma_tasklet+0x18/0x1c)
[<8027e594>] (mxs_dma_tasklet+0x18/0x1c) from [<8007d444>]
(tasklet_action+0x114/0x164)
-----------------------------------------------------------------
1.3) Assume the two DMA operations is X (first) and Y (second).
The root cause of the bug:
X's tasklet mxs_dma_tasklet trid to unmap the scatterlist, while Y is
trying to set up a new DMA operation with the _SAME_ scatterlist in
another ARM core.
[2] This patch adds a wait queue and two helpers gpmi_enter_dma/gpmi_exit_dma to
serialize all the DMA operations.
Signed-off-by: Huang Shijie <[email protected]>
Cc: [email protected]
---
drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 24 ++++++++++++++++++++++++
drivers/mtd/nand/gpmi-nand/gpmi-nand.h | 2 ++
2 files changed, 26 insertions(+), 0 deletions(-)
diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
index 71df69e..b849b92 100644
--- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
@@ -392,6 +392,20 @@ void prepare_data_dma(struct gpmi_nand_data *this, enum
dma_data_direction dr)
}
}
+static void gpmi_enter_dma(struct gpmi_nand_data *this)
+{
+ /* Wait until the previous DMA is finished. */
+ wait_event(this->dma_wait, !this->dma_is_working);
+
+ this->dma_is_working = true;
+}
+
+static void gpmi_exit_dma(struct gpmi_nand_data *this)
+{
+ this->dma_is_working = false;
+ wake_up(&this->dma_wait);
+}
+
/* This will be called after the DMA operation is finished. */
static void dma_irq_callback(void *param)
{
@@ -424,6 +438,7 @@ static void dma_irq_callback(void *param)
default:
pr_err("in wrong DMA operation.\n");
}
+ gpmi_exit_dma(this);
}
int start_dma_without_bch_irq(struct gpmi_nand_data *this,
@@ -906,6 +921,8 @@ static void gpmi_cmd_ctrl(struct mtd_info *mtd, int data,
unsigned int ctrl)
if (!this->command_length)
return;
+ gpmi_enter_dma(this);
+
ret = gpmi_send_command(this);
if (ret)
pr_err("Chip: %u, Error %d\n", this->current_chip, ret);
@@ -943,6 +960,8 @@ static void gpmi_read_buf(struct mtd_info *mtd, uint8_t
*buf, int len)
this->upper_buf = buf;
this->upper_len = len;
+ gpmi_enter_dma(this);
+
gpmi_read_data(this);
}
@@ -955,6 +974,8 @@ static void gpmi_write_buf(struct mtd_info *mtd, const
uint8_t *buf, int len)
this->upper_buf = (uint8_t *)buf;
this->upper_len = len;
+ gpmi_enter_dma(this);
+
gpmi_send_data(this);
}
@@ -1031,6 +1052,7 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd,
struct nand_chip *chip,
int ret;
pr_debug("page number is : %d\n", page);
+ gpmi_enter_dma(this);
ret = read_page_prepare(this, buf, mtd->writesize,
this->payload_virt, this->payload_phys,
nfc_geo->payload_size,
@@ -1107,6 +1129,7 @@ static int gpmi_ecc_write_page(struct mtd_info *mtd,
struct nand_chip *chip,
int ret;
pr_debug("ecc write page.\n");
+ gpmi_enter_dma(this);
if (this->swap_block_mark) {
/*
* If control arrives here, we're doing block mark swapping.
@@ -1745,6 +1768,7 @@ static int gpmi_nand_probe(struct platform_device *pdev)
platform_set_drvdata(pdev, this);
this->pdev = pdev;
this->dev = &pdev->dev;
+ init_waitqueue_head(&this->dma_wait);
ret = acquire_resources(this);
if (ret)
diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
index a7685e3..9597615 100644
--- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
+++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
@@ -160,6 +160,8 @@ struct gpmi_nand_data {
/* for DMA operations */
bool direct_dma_map_ok;
+ bool dma_is_working;
+ wait_queue_head_t dma_wait;
struct scatterlist cmd_sgl;
char *cmd_buffer;
--
1.7.2.rc3
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