[lkml]   [2018]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 1/2] serial: 8250: Don't service RX FIFO if interrupts are disabled
On Thu, Feb 8, 2018 at 2:55 PM, Vignesh R <> wrote:
> Currently, data in RX FIFO is read based on UART_LSR register state even
> if RDI and RLSI interrupts are disabled in UART_IER register.
> This is because when IRQ handler is called due to TX FIFO empty event,
> RX FIFO is serviced based on UART_LSR register status instead of
> UART_IIR status. This defeats the purpose of disabling UART RX
> FIFO interrupts during throttling(see, omap_8250_throttle()) as IRQ
> handler continues to drain UART RX FIFO resulting in overflow of buffer
> at tty layer.
> Fix this by making sure that driver drains UART RX FIFO only when
> UART_IIR_RDI is set along with UART_LSR_BI or UART_LSR_DR bits.
> Signed-off-by: Vignesh R <>

> - if (status & (UART_LSR_DR | UART_LSR_BI)) {
> + if (status & (UART_LSR_DR | UART_LSR_BI) &&
> + iir & UART_IIR_RDI) {

> if (!up->dma || handle_rx_dma(up, iir))

handle_rx_dma() checks for IRQ status as well.

But for now it seems we are on safe side since checks are done versus
IRQ status with bit 2 set, meaning that iir & RDI will be true.

> status = serial8250_rx_chars(up, status);
> }

Anyway, thanks for the patch, though I need some time to test it on
non-OMAP hardware with DMA enabled.

With Best Regards,
Andy Shevchenko

 \ /
  Last update: 2018-02-08 16:16    [W:0.044 / U:4.704 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site