Hi Alan,
Quoting One Thousand Gnomes <gno...@lxorguk.ukuu.org.uk>:
Maybe we should unset the low_latency flag as soon as DMA fails? There
are two flags, one is state->uart_port->flags and the other is
port->low_latency. I guess we need to unset both.
Well low latency and DMA are pretty much exclusive in the real world so
probably DMA ports shouldn't allow low_latency to be set at all in DMA
mode.
That's a useful insight. I assumed exactly the opposite.
But how should a real low_latency device work? Are they supported by
8250_core? Do they have hard IRQs? Are those IRQs handled by
serial8250_handle_irq()?
If DMA is not used, then serial8250_rx_chars() is the only way to
receive data. But serial8250_rx_chars() calls tty_flip_buffer_push()
unconditionally, and the later should not be called from the IRQ
context for low_latency devices, if the comment about it is to be
trusted.
--
Regards,
Pavel Roskin
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