Messages in this thread | | | Date | Wed, 23 Feb 2011 17:57:28 -0500 | From | Ted Ts'o <> | Subject | Re: How important is it that tty_write_room doesn't lie? |
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On Wed, Feb 23, 2011 at 02:48:18PM -0600, Timur Tabi wrote: > Greg KH wrote: > > I think that people don't normally hit this as the console code isn't > > used as a tty and a console at the same time, right? > > That's another thing I never understood. It's rare for a driver to > support both the console and tty layers. The serial core driver > does that, but I can't find any other examples. I would think that > a driver would support both interfaces, because both are needed. > Simplistically, printk --> console, and printf --> tty. When would > ever want user-space support but not kernel support?
When you are supporting a large bank of modems? A number of the serial cards were originally created to support 32, 64, 128 serial ports per PCI board, specifically to drive modems, in the bad old days of modems. :-)
And I suspect many modern serial devices are just 8250/16550A based, so they get the console and userspace serial for free. A large number of the more exotic boards were created because the 16550A uart isn't ideal if you are driving vast number of modems at the same time.
> The FIFO can vary, but it's probably at least 2KB it size. At > least, we hope to able to set it to that size in the field. > Currently, we set it to 4KB.
Wow, the FIFO has gotten a lot larger than I ever remember them getting even when people were doing 460kbps. I'm guessing this is because you're trying to defer interrupts for power saving reasons, yes? I was used to seeing FIFO sizes more in the 32-128 bytes, tops. :-)
- Ted
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