Messages in this thread | | | Date | Tue, 14 Jan 2014 11:24:57 -0500 | From | Pavel Roskin <> | Subject | Re: serial8250: bogus low_latency destabilizes kernel, need sanity check |
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Hi Alan,
Quoting One Thousand Gnomes <gnomes@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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