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于 2012年04月26日 19:11, Russell King - ARM Linux 写道:
The UART uses the DMA for RX/TX with the hardware flow control (RTS/CTS) enabled all the time.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
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.
The uart uses the SDMA (drivers/dma/imx-sdma.c). And the SDMA may schedule out in :.../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?
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 -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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