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SubjectRe: Writing a console/tty driver -- how to use tty_port?
On Wed, 27 Oct 2010 16:04:13 -0500
Timur Tabi <timur@freescale.com> wrote:

> Greg,
>
> Do you have an updated version of Tiny TTY that uses tty_port structures? I'm
> trying to write a new TTY driver for a device that is not a UART, and I'm having
> a hard time finding a good example. I suspect I need to understand the tty_port
> structure, but I can't find any documentation for it.
>
> One specific problem I'm having is that I can't figure out how to get a
> tty_struct pointer in my interrupt handler. The ISR gets called whenever there
> is new input, and it needs to call tty_insert_flip_string(). But it appears
> that it's possible to have my driver opened multiple times, each time creating a
> new TTY. But since I can only have one interrupt handler, I don't know how to
> determine which of the tty_structs to use. I figure tty_port is a way to
> resolve this problem, but I don't know how to use it exactly.

You only have one tty struct for the multiple opens.

Basically

tty_port - lifetime of hardware being loaded
tty_struct - lifetime open/close (and a bit
beyond for refs)


So you can use tty_port_tty_get() which also knows about all the ghastly
internal locking rules.

Eventually the rx buffer should be moved to the tty_port which will make
the world vastly saner.

drivers/mmc/card/sdio_uart.c

is in some ways the best example, it handles all the horrible cases
including unloading of hardware v open races, its way more than you'd
need but does illustrate it all.

I've also got a draft tty_kfifo layer which is designed to be tty_port
with kfifo queues as a helper. Remind me next week if it would be useful
and I'll dig it back out.

Alan


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