read for serial driver

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Bhavin Shah Contact options for registered users 's Avatar (by Gravatar) posted on
March 5, 2004, 11:23 am
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I am writing a serial driver on Linux –2.4.18-rmk7-pxa1. I was going
through the source code and I found that the device specific driver
does not implemen the 'read' function. The interrupt handler of the
device specific driver copies the character read in to
tty->flip.char_buf_ptr and then calls 'tty_flip_buffer_push' function.
I checked from the 'tty_read' function and it calles 'tty->ldisc.read'
function call.

My question is, when the user calls the 'read' call on say /dev/ttyS0
from which read function the character is actually read. If someone
could give me the function trace it would be great. Also, I could not
find out what is this 'tty->ldisc.read' function and from where is it
coming?

Any help in this area is highly appreciated.

Thanks,
Bhavin

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Grant Edwards Contact options for registered users 's Avatar (by Gravatar) posted on
March 5, 2004, 2:51 pm
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Re: read for serial driver

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It's read from the tty layer's receive buffer.  That's where it
goes after you put it in the flip buffer and push it.

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Huh?  Function trace of what? The tty I/O module's read()
function?

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IIRC it's a pointer.  Look for places where it's set.  If
you're just writing a low-level serial driver, you don't need
to worry about it.  All you need to do is put the receive data
in the flip buffer.

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