RE: [PATCH 4/4] serial: xuartps: Rewrite the interrupt handling logic

[Anirudha Sarangi]

Hi,

> -----Original Message-----
> From: Peter Hurley [mailto:peter@xxxxxxxxxxxxxxxxxx]
> Sent: Monday, August 17, 2015 9:26 PM
> To: Michal Simek
> Cc: linux-kernel@xxxxxxxxxxxxxxx; monstr@xxxxxxxxx; Anirudha Sarangi; Soren
> Brinkmann; Jiri Slaby; linux-serial@xxxxxxxxxxxxxxx; Greg Kroah-Hartman; linux-
> arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH 4/4] serial: xuartps: Rewrite the interrupt handling logic
>
> On 08/17/2015 03:22 AM, Michal Simek wrote:
> > From: Anirudha Sarangi <anirudha.sarangi@xxxxxxxxxx>
> >
> > The existing interrupt handling logic has followins issues.
> > - Upon a parity error with default configuration, the control
> >   never comes out of the ISR thereby hanging Linux.
> > - The error handling logic around framing and parity error are buggy.
> >   There are chances that the errors will never be captured.
> > - The existing ISR is just too long.
> > This patch fixes all these concerns.
>
> This patch is unreviewable. Please break this down into multiple patches.
>
Thanks. Let me give a shot. It is just breaking the single big ISR that has both Rx and Tx in a single function into smaller ones.
Not sure how I will create smaller patches, but I will try and get back.

Regards
Anirudha

> Regards,
> Peter Hurley
>
> > It separates out the Tx and Rx
> > hanling logic into separate functions. It ensures that the status
> > registers are cleared on all cases so that a hang situation never
> > arises.
> >
> > Signed-off-by: Anirudha Sarangi <anirudh@xxxxxxxxxx>
> > Signed-off-by: Michal Simek <michal.simek@xxxxxxxxxx>
> > ---
> >
> >  drivers/tty/serial/xilinx_uartps.c | 194
> > ++++++++++++++++++++-----------------
> >  1 file changed, 104 insertions(+), 90 deletions(-)
> >
> > diff --git a/drivers/tty/serial/xilinx_uartps.c
> > b/drivers/tty/serial/xilinx_uartps.c
> > index 2dc26e5f1384..c771dbbf6161 100644
> > --- a/drivers/tty/serial/xilinx_uartps.c
> > +++ b/drivers/tty/serial/xilinx_uartps.c
> > @@ -173,61 +173,86 @@ struct cdns_uart {
> >             clk_rate_change_nb);
> >
> >  /**
> > - * cdns_uart_isr - Interrupt handler
> > - * @irq: Irq number
> > - * @dev_id: Id of the port
> > - *
> > - * Return: IRQHANDLED
> > + * cdns_uart_handle_tx - Handle the bytes to be Txed.
> > + * @dev_id: Id of the UART port
> > + * Return: None
> >   */
> > -static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
> > +static void cdns_uart_handle_tx(void *dev_id)
> >  {
> >     struct uart_port *port = (struct uart_port *)dev_id;
> > -   unsigned long flags;
> > -   unsigned int isrstatus, numbytes;
> > -   unsigned int data;
> > -   char status = TTY_NORMAL;
> > +   unsigned int numbytes;
> >
> > -   spin_lock_irqsave(&port->lock, flags);
> > +   if (uart_circ_empty(&port->state->xmit)) {
> > +           writel(CDNS_UART_IXR_TXEMPTY, port->membase +
> > +                  CDNS_UART_IDR_OFFSET);
> > +   } else {
> > +           numbytes = port->fifosize;
> > +           /* Break if no more data available in the UART buffer */
> > +           while (numbytes--) {
> > +                   if (uart_circ_empty(&port->state->xmit))
> > +                           break;
> > +                   /*
> > +                    * Get the data from the UART circular buffer
> > +                    * and write it to the cdns_uart's TX_FIFO
> > +                    * register.
> > +                    */
> > +                   writel(port->state->xmit.buf[port->state->xmit.tail],
> > +                          port->membase + CDNS_UART_FIFO_OFFSET);
> >
> > -   /* Read the interrupt status register to determine which
> > -    * interrupt(s) is/are active.
> > -    */
> > -   isrstatus = readl(port->membase + CDNS_UART_ISR_OFFSET);
> > +                   port->icount.tx++;
> >
> > -   /*
> > -    * There is no hardware break detection, so we interpret framing
> > -    * error with all-zeros data as a break sequence. Most of the time,
> > -    * there's another non-zero byte at the end of the sequence.
> > -    */
> > -   if (isrstatus & CDNS_UART_IXR_FRAMING) {
> > -           while (!(readl(port->membase + CDNS_UART_SR_OFFSET) &
> > -                                   CDNS_UART_SR_RXEMPTY)) {
> > -                   if (!readl(port->membase + CDNS_UART_FIFO_OFFSET))
> {
> > -                           port->read_status_mask |=
> CDNS_UART_IXR_BRK;
> > -                           isrstatus &= ~CDNS_UART_IXR_FRAMING;
> > -                   }
> > +                   /*
> > +                    * Adjust the tail of the UART buffer and wrap
> > +                    * the buffer if it reaches limit.
> > +                    */
> > +                   port->state->xmit.tail =
> > +                           (port->state->xmit.tail + 1) &
> > +                                   (UART_XMIT_SIZE - 1);
> >             }
> > -           writel(CDNS_UART_IXR_FRAMING,
> > -                           port->membase + CDNS_UART_ISR_OFFSET);
> > -   }
> >
> > -   /* drop byte with parity error if IGNPAR specified */
> > -   if (isrstatus & port->ignore_status_mask & CDNS_UART_IXR_PARITY)
> > -           isrstatus &= ~(CDNS_UART_IXR_RXTRIG |
> CDNS_UART_IXR_TOUT);
> > +           if (uart_circ_chars_pending(
> > +                           &port->state->xmit) < WAKEUP_CHARS)
> > +                   uart_write_wakeup(port);
> > +   }
> > +}
> >
> > -   isrstatus &= port->read_status_mask;
> > -   isrstatus &= ~port->ignore_status_mask;
> > +/**
> > + * cdns_uart_handle_rx - Handle the received bytes along with Rx errors.
> > + * @dev_id: Id of the UART port
> > + * @isrstatus: The interrupt status register value as read
> > + * Return: None
> > + */
> > +static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
> > +{
> > +   struct uart_port *port = (struct uart_port *)dev_id;
> > +   unsigned int data;
> > +   unsigned int framerrprocessed = 0;
> > +   char status = TTY_NORMAL;
> >
> > -   if ((isrstatus & CDNS_UART_IXR_TOUT) ||
> > -           (isrstatus & CDNS_UART_IXR_RXTRIG)) {
> > -           /* Receive Timeout Interrupt */
> > -           while (!(readl(port->membase + CDNS_UART_SR_OFFSET) &
> > -                                   CDNS_UART_SR_RXEMPTY)) {
> > -                   data = readl(port->membase +
> CDNS_UART_FIFO_OFFSET);
> > +   while ((readl(port->membase + CDNS_UART_SR_OFFSET) &
> > +           CDNS_UART_SR_RXEMPTY) != CDNS_UART_SR_RXEMPTY) {
> > +           data = readl(port->membase + CDNS_UART_FIFO_OFFSET);
> > +           port->icount.rx++;
> > +           /*
> > +            * There is no hardware break detection, so we interpret
> > +            * framing error with all-zeros data as a break sequence.
> > +            * Most of the time, there's another non-zero byte at the
> > +            * end of the sequence.
> > +            */
> > +           if (isrstatus & CDNS_UART_IXR_FRAMING) {
> > +                   if (!data) {
> > +                           port->read_status_mask |=
> CDNS_UART_IXR_BRK;
> > +                           framerrprocessed = 1;
> > +                           continue;
> > +                   }
> > +           }
> > +           isrstatus &= port->read_status_mask;
> > +           isrstatus &= ~port->ignore_status_mask;
> >
> > -                   /* Non-NULL byte after BREAK is garbage (99%) */
> > -                   if (data && (port->read_status_mask &
> > -                                           CDNS_UART_IXR_BRK)) {
> > +           if ((isrstatus & CDNS_UART_IXR_TOUT) ||
> > +               (isrstatus & CDNS_UART_IXR_RXTRIG)) {
> > +                   if (data &&
> > +                       (port->read_status_mask & CDNS_UART_IXR_BRK)) {
> >                             port->read_status_mask &=
> ~CDNS_UART_IXR_BRK;
> >                             port->icount.brk++;
> >                             if (uart_handle_break(port))
> > @@ -249,67 +274,56 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
> >                             spin_lock(&port->lock);
> >                     }
> >  #endif
> > -
> > -                   port->icount.rx++;
> > -
> >                     if (isrstatus & CDNS_UART_IXR_PARITY) {
> >                             port->icount.parity++;
> >                             status = TTY_PARITY;
> > -                   } else if (isrstatus & CDNS_UART_IXR_FRAMING) {
> > +                   }
> > +                   if ((isrstatus & CDNS_UART_IXR_FRAMING) &&
> > +                       !framerrprocessed) {
> >                             port->icount.frame++;
> >                             status = TTY_FRAME;
> > -                   } else if (isrstatus & CDNS_UART_IXR_OVERRUN) {
> > +                   }
> > +                   if (isrstatus & CDNS_UART_IXR_OVERRUN) {
> >                             port->icount.overrun++;
> > +                           tty_insert_flip_char(&port->state->port, 0,
> > +                                                TTY_OVERRUN);
> >                     }
> > -
> > -                   uart_insert_char(port, isrstatus,
> CDNS_UART_IXR_OVERRUN,
> > -                                   data, status);
> > +                   tty_insert_flip_char(&port->state->port, data, status);
> >             }
> > -           spin_unlock(&port->lock);
> > -           tty_flip_buffer_push(&port->state->port);
> > -           spin_lock(&port->lock);
> >     }
> > +   spin_unlock(&port->lock);
> > +   tty_flip_buffer_push(&port->state->port);
> > +   spin_lock(&port->lock);
> > +}
> >
> > -   /* Dispatch an appropriate handler */
> > -   if ((isrstatus & CDNS_UART_IXR_TXEMPTY) ==
> CDNS_UART_IXR_TXEMPTY) {
> > -           if (uart_circ_empty(&port->state->xmit)) {
> > -                   writel(CDNS_UART_IXR_TXEMPTY,
> > -                                   port->membase +
> CDNS_UART_IDR_OFFSET);
> > -           } else {
> > -                   numbytes = port->fifosize;
> > -                   /* Break if no more data available in the UART buffer */
> > -                   while (numbytes--) {
> > -                           if (uart_circ_empty(&port->state->xmit))
> > -                                   break;
> > -                           /* Get the data from the UART circular buffer
> > -                            * and write it to the cdns_uart's TX_FIFO
> > -                            * register.
> > -                            */
> > -                           writel(port->state->xmit.buf[
> > -                                           port->state->xmit.tail],
> > -                                   port->membase +
> CDNS_UART_FIFO_OFFSET);
> > -
> > -                           port->icount.tx++;
> > -
> > -                           /* Adjust the tail of the UART buffer and wrap
> > -                            * the buffer if it reaches limit.
> > -                            */
> > -                           port->state->xmit.tail =
> > -                                   (port->state->xmit.tail + 1) &
> > -                                           (UART_XMIT_SIZE - 1);
> > -                   }
> > +/**
> > + * cdns_uart_isr - Interrupt handler
> > + * @irq: Irq number
> > + * @dev_id: Id of the port
> > + *
> > + * Return: IRQHANDLED
> > + */
> > +static irqreturn_t cdns_uart_isr(int irq, void *dev_id) {
> > +   struct uart_port *port = (struct uart_port *)dev_id;
> > +   unsigned int isrstatus;
> >
> > -                   if (uart_circ_chars_pending(
> > -                                   &port->state->xmit) < WAKEUP_CHARS)
> > -                           uart_write_wakeup(port);
> > -           }
> > -   }
> > +   spin_lock(&port->lock);
> >
> > +   /* Read the interrupt status register to determine which
> > +    * interrupt(s) is/are active and clear them.
> > +    */
> > +   isrstatus = readl(port->membase + CDNS_UART_ISR_OFFSET);
> >     writel(isrstatus, port->membase + CDNS_UART_ISR_OFFSET);
> >
> > -   /* be sure to release the lock and tty before leaving */
> > -   spin_unlock_irqrestore(&port->lock, flags);
> > +   if (isrstatus & CDNS_UART_IXR_TXEMPTY) {
> > +           cdns_uart_handle_tx(dev_id);
> > +           isrstatus &= ~CDNS_UART_IXR_TXEMPTY;
> > +   }
> > +   if (isrstatus & CDNS_UART_IXR_MASK)
> > +           cdns_uart_handle_rx(dev_id, isrstatus);
> >
> > +   spin_unlock(&port->lock);
> >     return IRQ_HANDLED;
> >  }
> >
> >



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