于 2012年04月26日 19:11, Russell King - ARM Linux 写道:
On Thu, Apr 26, 2012 at 06:37:11PM +0800, Huang Shijie wrote:
Add the DMA support for uart RX and TX.
Signed-off-by: Huang Shijie<b32955@xxxxxxxxxxxxx>
---
Apart from the comments below,
1. How do you deal with transmitting the high-priority XON/XOFF
characters (port->x_char) which occur with s/w flow control and
the tty buffers fill up?
2. How do you deal with flow control in general? IOW, what happens
when the remote end deasserts your CTS with h/w flow control enabled.
How does your end deal with sending RTS according to flow control
conditions?
i
The UART uses the DMA for RX/TX with the hardware flow control (RTS/CTS)
enabled all the time.
If we use the software flow control(XON/XOFF), we should not enable the DMA.
I think i should add more comments about this issue.
For example:
The MX6Q arm2 has two uarts, one with the DMA disabled is used for debug,
the other one with the DMA/RTS.CTS enabled can be used for the Bluetooth.
.../bindings/tty/serial/fsl-imx-uart.txt | 7 +
drivers/tty/serial/imx.c | 386 +++++++++++++++++++-
2 files changed, 389 insertions(+), 4 deletions(-)
diff --git a/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt b/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
index a9c0406..f27489d 100644
--- a/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
+++ b/Documentation/devicetree/bindings/tty/serial/fsl-imx-uart.txt
@@ -8,6 +8,10 @@ Required properties:
Optional properties:
- fsl,uart-has-rtscts : Indicate the uart has rts and cts
- fsl,irda-mode : Indicate the uart supports irda mode
+- fsl,enable-dma : Indicate the uart supports DMA
+- fsl,uart-dma-events : contains the DMA events for RX and TX,
+ The first is the RX event, while the other is TX.
+- fsl,enable-dte: Indicate the uart works in DTE mode
Example:
@@ -16,4 +20,7 @@ uart@73fbc000 {
reg =<0x73fbc000 0x4000>;
interrupts =<31>;
fsl,uart-has-rtscts;
+ fsl,enable-dma;
+ fsl,uart-dma-events =<xx xx>;
+ fsl,enable-dte;
};
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index e7fecee..65ba24d 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -47,9 +47,11 @@
#include<linux/slab.h>
#include<linux/of.h>
#include<linux/of_device.h>
+#include<linux/dma-mapping.h>
#include<asm/io.h>
#include<asm/irq.h>
+#include<mach/dma.h>
#include<mach/imx-uart.h>
/* Register definitions */
@@ -82,6 +84,7 @@
#define UCR1_ADBR (1<<14) /* Auto detect baud rate */
#define UCR1_TRDYEN (1<<13) /* Transmitter ready interrupt enable */
#define UCR1_IDEN (1<<12) /* Idle condition interrupt */
+#define UCR1_ICD_REG(x) (((x)& 3)<< 10) /* idle condition detect */
#define UCR1_RRDYEN (1<<9) /* Recv ready interrupt enable */
#define UCR1_RDMAEN (1<<8) /* Recv ready DMA enable */
#define UCR1_IREN (1<<7) /* Infrared interface enable */
@@ -125,6 +128,7 @@
#define UCR4_ENIRI (1<<8) /* Serial infrared interrupt enable */
#define UCR4_WKEN (1<<7) /* Wake interrupt enable */
#define UCR4_REF16 (1<<6) /* Ref freq 16 MHz */
+#define UCR4_IDDMAEN (1<<6) /* DMA IDLE Condition Detected */
#define UCR4_IRSC (1<<5) /* IR special case */
#define UCR4_TCEN (1<<3) /* Transmit complete interrupt enable */
#define UCR4_BKEN (1<<2) /* Break condition interrupt enable */
@@ -134,6 +138,7 @@
#define UFCR_RFDIV (7<<7) /* Reference freq divider mask */
#define UFCR_RFDIV_REG(x) (((x)< 7 ? 6 - (x) : 6)<< 7)
#define UFCR_TXTL_SHF 10 /* Transmitter trigger level shift */
+#define UFCR_DCEDTE (1<<6)
#define USR1_PARITYERR (1<<15) /* Parity error interrupt flag */
#define USR1_RTSS (1<<14) /* RTS pin status */
#define USR1_TRDY (1<<13) /* Transmitter ready interrupt/dma flag */
@@ -200,12 +205,27 @@ struct imx_port {
unsigned int old_status;
int txirq,rxirq,rtsirq;
unsigned int have_rtscts:1;
+ unsigned int enable_dte:1;
+ unsigned int enable_dma:1;
unsigned int use_irda:1;
unsigned int irda_inv_rx:1;
unsigned int irda_inv_tx:1;
unsigned short trcv_delay; /* transceiver delay */
struct clk *clk;
struct imx_uart_data *devdata;
+
+ /* DMA fields */
+ unsigned int dma_req_rx;
+ unsigned int dma_req_tx;
+ struct imx_dma_data dma_data;
+ struct dma_chan *dma_chan_rx, *dma_chan_tx;
+ struct scatterlist rx_sgl, tx_sgl[2];
+ void *rx_buf;
+ unsigned int rx_bytes, tx_bytes;
+ struct work_struct tsk_dma_rx, tsk_dma_tx;
Why do you need a work struct to deal with DMA?
The uart uses the SDMA (drivers/dma/imx-sdma.c). And the SDMA may
schedule out in :
sdma_prep_slave_sg() --> sdma_load_contex() -->sdma_run_channel() .
So i have to add a work struct to prepare and triger the DMA operations.
+ unsigned int dma_tx_nents;
+ bool dma_is_rxing;
+ wait_queue_head_t dma_wait;
};
struct imx_port_ucrs {
@@ -394,6 +414,13 @@ static void imx_stop_rx(struct uart_port *port)
struct imx_port *sport = (struct imx_port *)port;
unsigned long temp;
+ /*
+ * We are maybe in the SMP now, so if the DMA RX thread is running,
+ * we have to wait for it to finish.
+ */
+ if (sport->enable_dma&& sport->dma_is_rxing)
+ return;
+
temp = readl(sport->port.membase + UCR2);
writel(temp&~ UCR2_RXEN, sport->port.membase + UCR2);
}
@@ -429,6 +456,80 @@ static inline void imx_transmit_buffer(struct imx_port *sport)
imx_stop_tx(&sport->port);
}
+static void dma_tx_callback(void *data)
+{
+ struct imx_port *sport = data;
+ struct scatterlist *sgl =&sport->tx_sgl[0];
struct scatterlist *sgl = sport->tx_sgl;
is equivalent, and less typing.
+ struct circ_buf *xmit =&sport->port.state->xmit;
+
+ dma_unmap_sg(sport->port.dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
+
+ /* update the stat */
+ spin_lock(&sport->port.lock);
+ xmit->tail = (xmit->tail + sport->tx_bytes)& (UART_XMIT_SIZE - 1);
+ sport->port.icount.tx += sport->tx_bytes;
+ spin_unlock(&sport->port.lock);
Callbacks are called from tasklet context, and will have IRQs enabled.
As the port lock is taken from IRQ context, this is waiting for a deadlock
to happen. Have you run this with lockdep enabled?
This callback is called from IRQ context, with all the IRQ disabled. see:
sdma_int_handler() -->mxc_sdma_handle_channel() -->
mxc_sdma_handle_channel_normal()
--> .callback().
So spin_lock() is enough.
Best Regards
Huang Shijie
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