From: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@xxxxxxxxxxx>
This patch fixes the problem that an interrupt may set up a new I2C
message and the DMA callback overwrites this setup.
By disabling the DMA Enable Register(ICDMAER), rcar_i2c_dma_unmap()
enables interrupts for register settings (such as Master Control
Register(ICMCR)) and advances the I2C transfer sequence.
If an interrupt occurs immediately after ICDMAER is disabled, the
callback handler later continues and overwrites the previous settings
from the interrupt. So, disable ICDMAER at the end of the callback to
ensure other interrupts are masked until then.
Note that this driver needs to work lock-free because there are IP cores
with a HW race condition which prevent us from using a spinlock in the
interrupt handler.
Reproduction test:
1. Add udelay(1) after disabling ICDMAER. (It is expected to
generate an interrupt of rcar_i2c_irq())
void rcar_i2c_dma_unmap(struct rcar_i2c_priv *priv)
{
...
rcar_i2c_write(priv, ICDMAER, 0);
udelay(1); <-- Add this line
...
priv->dma_direction = DMA_NONE;
}
2. Execute DMA transfer.
Performs DMA transfer of read or write. In the sample, write was used.
$ i2cset -y -f 4 0x6a 0x01 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 i
3. A log message of BUG_ON() will be displayed.
Signed-off-by: Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@xxxxxxxxxxx>
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
---
drivers/i2c/busses/i2c-rcar.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index dd52a068b140..6410896f717b 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -363,9 +363,6 @@ static void rcar_i2c_dma_unmap(struct rcar_i2c_priv *priv)
struct dma_chan *chan = priv->dma_direction == DMA_FROM_DEVICE
? priv->dma_rx : priv->dma_tx;
- /* Disable DMA Master Received/Transmitted */
- rcar_i2c_write(priv, ICDMAER, 0);
-
dma_unmap_single(chan->device->dev, sg_dma_address(&priv->sg),
sg_dma_len(&priv->sg), priv->dma_direction);
@@ -375,6 +372,9 @@ static void rcar_i2c_dma_unmap(struct rcar_i2c_priv *priv)
priv->flags |= ID_P_NO_RXDMA;
priv->dma_direction = DMA_NONE;
+
+ /* Disable DMA Master Received/Transmitted */
+ rcar_i2c_write(priv, ICDMAER, 0);
}
static void rcar_i2c_cleanup_dma(struct rcar_i2c_priv *priv)
--
2.11.0
