On Fri, Apr 27, 2012 at 09:22:45AM +0100, Russell King - ARM Linux wrote: > On Fri, Apr 27, 2012 at 03:00:39PM +0800, Huang Shijie wrote: > > 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. > > Your answer is too vague. Please try again. > > > 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() . > > It should not. prep_slave_sg() must be callable from atomic contexts. I just sent out a patch to fix it. [PATCH 01/11] dma: imx-sdma: make channel0 operations atomic Thanks Richard > > > 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(). > > That's a bug in your dmaengine driver. > -- 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