Re: serial: start_tx & buffer handling
On Fri, May 4, 2018 at 5:44 PM, loïc tourlonias wrote: > Hi > > On Fri, May 4, 2018 at 6:31 AM, Muni Sekhar wrote: >>> >>> On Fri, May 4, 2018 at 12:04 AM, Greg KH wrote: >>> > On Thu, May 03, 2018 at 08:08:48PM +0530, Muni Sekhar wrote: >>> >> Hi All, >>> >> >>> >> I’m trying to understand how user mode buffer is written to low level >>> >> serial hardware registers. >>> >> >>> >> For this I read the kernel code and I came to know that from user mode >>> >> write() API lands into kernel’s tty_write() ("drivers/tty/tty_io.c") >>> >> and then it calls a uart_write() ("drivers/tty/serial/serial_core.c"). >>> >> >>> >> In uart_write(), the buffer is copied to circ_buf and then it calls >>> >> low level serial hardware driver’s start_tx() (struct uart_ops >>> >> .start_tx). But here I could not find how the buffer kept in circ_buf >>> >> is copied to serial port’s TX_FIFO registers? >>> >> >>> >> Can someone take a moment to explain me on this? >>> > >>> > It all depends on which specific UART driver you are looking at, they >>> > all do it a bit different depending on the hardware. >>> > >>> > Which one are you looking at? Look at what the start_tx callback does >>> > for that specific driver, that should give you a hint as to how data >>> > starts flowing. Usually an interrupt is enabled that is used to flush >>> > the buffer out to the hardware. >>> > >>> >>> I’m looking for any existing sample code which does DMA transfers of >>> UART transmitted data. I looked at the bcm63xx_uart.c, it looks it >>> does not handle DMA transfers. Even copying the Tx buffer (from >>> circ_buf) to UART_FIFO_REG happening in ISR. > > > You can have a look at atmel_serial kernel module (built for ARM). > > https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/atmel_serial.c > > The dma buffer is linked to uart circular buffer in prepare_tx() function > called from uart_startup(). It's released in release_tx() function called > from uart_shutdown(). DMA buffer is managed in schedule_tx() function called > from a tasklet triggered by the ISR. Thanks a lot for this information. > > HTH > >>> >>> >>> > thanks, >>> > >>> > greg k-h >>> >>> >>> >>> -- >>> Thanks, >>> Sekhar >>> >>> ___ >>> Kernelnewbies mailing list >>> Kernelnewbies@kernelnewbies.org >>> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> -- Thanks, Sekhar ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: serial: start_tx & buffer handling
Hi On Fri, May 4, 2018 at 6:31 AM, Muni Sekhar wrote: >> >> On Fri, May 4, 2018 at 12:04 AM, Greg KH wrote: >> > On Thu, May 03, 2018 at 08:08:48PM +0530, Muni Sekhar wrote: >> >> Hi All, >> >> >> >> I’m trying to understand how user mode buffer is written to low level >> >> serial hardware registers. >> >> >> >> For this I read the kernel code and I came to know that from user mode >> >> write() API lands into kernel’s tty_write() ("drivers/tty/tty_io.c") >> >> and then it calls a uart_write() ("drivers/tty/serial/serial_core.c"). >> >> >> >> In uart_write(), the buffer is copied to circ_buf and then it calls >> >> low level serial hardware driver’s start_tx() (struct uart_ops >> >> .start_tx). But here I could not find how the buffer kept in circ_buf >> >> is copied to serial port’s TX_FIFO registers? >> >> >> >> Can someone take a moment to explain me on this? >> > >> > It all depends on which specific UART driver you are looking at, they >> > all do it a bit different depending on the hardware. >> > >> > Which one are you looking at? Look at what the start_tx callback does >> > for that specific driver, that should give you a hint as to how data >> > starts flowing. Usually an interrupt is enabled that is used to flush >> > the buffer out to the hardware. >> > >> >> I’m looking for any existing sample code which does DMA transfers of >> UART transmitted data. I looked at the bcm63xx_uart.c, it looks it >> does not handle DMA transfers. Even copying the Tx buffer (from >> circ_buf) to UART_FIFO_REG happening in ISR. You can have a look at atmel_serial kernel module (built for ARM). https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/atmel_serial.c The dma buffer is linked to uart circular buffer in prepare_tx() function called from uart_startup(). It's released in release_tx() function called from uart_shutdown(). DMA buffer is managed in schedule_tx() function called from a tasklet triggered by the ISR. HTH >> >> >> > thanks, >> > >> > greg k-h >> >> >> >> -- >> Thanks, >> Sekhar >> >> ___ >> Kernelnewbies mailing list >> Kernelnewbies@kernelnewbies.org >> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: serial: start_tx & buffer handling
Hi On Fri, May 4, 2018 at 6:31 AM, Muni Sekhar wrote: > On Fri, May 4, 2018 at 12:04 AM, Greg KH wrote: > > On Thu, May 03, 2018 at 08:08:48PM +0530, Muni Sekhar wrote: > >> Hi All, > >> > >> I’m trying to understand how user mode buffer is written to low level > >> serial hardware registers. > >> > >> For this I read the kernel code and I came to know that from user mode > >> write() API lands into kernel’s tty_write() ("drivers/tty/tty_io.c") > >> and then it calls a uart_write() ("drivers/tty/serial/serial_core.c"). > >> > >> In uart_write(), the buffer is copied to circ_buf and then it calls > >> low level serial hardware driver’s start_tx() (struct uart_ops > >> .start_tx). But here I could not find how the buffer kept in circ_buf > >> is copied to serial port’s TX_FIFO registers? > >> > >> Can someone take a moment to explain me on this? > > > > It all depends on which specific UART driver you are looking at, they > > all do it a bit different depending on the hardware. > > > > Which one are you looking at? Look at what the start_tx callback does > > for that specific driver, that should give you a hint as to how data > > starts flowing. Usually an interrupt is enabled that is used to flush > > the buffer out to the hardware. > > > > I’m looking for any existing sample code which does DMA transfers of > UART transmitted data. I looked at the bcm63xx_uart.c, it looks it > does not handle DMA transfers. Even copying the Tx buffer (from > circ_buf) to UART_FIFO_REG happening in ISR. > You can have a look at atmel_serial kernel module (built for ARM). https://elixir.bootlin.com/linux/latest/source/drivers/tty/serial/atmel_serial.c The dma buffer is linked to uart circular buffer in prepare_tx() function called from uart_startup(). It's released in release_tx() function called from uart_shutdown(). DMA buffer is managed in schedule_tx() function called from a tasklet triggered by the ISR. HTH > > > > thanks, > > > > greg k-h > > > > -- > Thanks, > Sekhar > > ___ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: serial: start_tx & buffer handling
On Fri, May 4, 2018 at 12:04 AM, Greg KH wrote: > On Thu, May 03, 2018 at 08:08:48PM +0530, Muni Sekhar wrote: >> Hi All, >> >> I’m trying to understand how user mode buffer is written to low level >> serial hardware registers. >> >> For this I read the kernel code and I came to know that from user mode >> write() API lands into kernel’s tty_write() ("drivers/tty/tty_io.c") >> and then it calls a uart_write() ("drivers/tty/serial/serial_core.c"). >> >> In uart_write(), the buffer is copied to circ_buf and then it calls >> low level serial hardware driver’s start_tx() (struct uart_ops >> .start_tx). But here I could not find how the buffer kept in circ_buf >> is copied to serial port’s TX_FIFO registers? >> >> Can someone take a moment to explain me on this? > > It all depends on which specific UART driver you are looking at, they > all do it a bit different depending on the hardware. > > Which one are you looking at? Look at what the start_tx callback does > for that specific driver, that should give you a hint as to how data > starts flowing. Usually an interrupt is enabled that is used to flush > the buffer out to the hardware. > I’m looking for any existing sample code which does DMA transfers of UART transmitted data. I looked at the bcm63xx_uart.c, it looks it does not handle DMA transfers. Even copying the Tx buffer (from circ_buf) to UART_FIFO_REG happening in ISR. > thanks, > > greg k-h -- Thanks, Sekhar ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: serial: start_tx & buffer handling
On Thu, May 03, 2018 at 08:08:48PM +0530, Muni Sekhar wrote: > Hi All, > > I’m trying to understand how user mode buffer is written to low level > serial hardware registers. > > For this I read the kernel code and I came to know that from user mode > write() API lands into kernel’s tty_write() ("drivers/tty/tty_io.c") > and then it calls a uart_write() ("drivers/tty/serial/serial_core.c"). > > In uart_write(), the buffer is copied to circ_buf and then it calls > low level serial hardware driver’s start_tx() (struct uart_ops > .start_tx). But here I could not find how the buffer kept in circ_buf > is copied to serial port’s TX_FIFO registers? > > Can someone take a moment to explain me on this? It all depends on which specific UART driver you are looking at, they all do it a bit different depending on the hardware. Which one are you looking at? Look at what the start_tx callback does for that specific driver, that should give you a hint as to how data starts flowing. Usually an interrupt is enabled that is used to flush the buffer out to the hardware. thanks, greg k-h ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies