Re: Linux tty layer hackery: Heads up and RFC

[Mark Underwood <basicmark@yahoo.com>]

Hi Rogier,

Having just written a DMA UART driver I can say this
is good news :-). Here are some things to think about:

What my driver would like to do is to handle its own
input buffers. It would pass the buffer to the tty
layer when it is full and the tty layer would pass the
buffer back once it has drained the data from it.
The problem is that I don't always receive a block
worth of characters so I also need to pass the tty
layer a buffer (which I'm still DMAing into) with a
count of how many chars there are in the buffer and a
offset of where to start from. If I can't do this then
I have to stop the DMA transfer, pass you a mostly
empty buffer with a char count, and setup DMA transfer
into another buffer. If during this I get a burst of
data I could well lose it :-(.

Best Regards,

Mark

--- Rogier Wolff <R.E.Wolff@BitWizard.nl> wrote:

> On Thu, Jul 21, 2005 at 06:46:32PM +0100, Alan Cox
> wrote:
> > int tty_prepare_flip_string(tty, strptr, len)
> > 
> > Adjust the buffer to allow len characters to be
> added. Returns a buffer
> > pointer in strptr and the length available. This
> allows for hardware
> > that needs to use functions like insl or
> mencpy_fromio.
> 
> Ok, So then I start copying characters into the
> flipstring, but how do
> I say I'm done?
> 
> Or is there a race between that I call
> tty_prepare_flip_string, and
> other processes start pulling my not-yet-filled
> string from the
> buffer? (Surely not!)
> 
> 	Roger. 
> 
> -- 
> ** R.E.Wolff@BitWizard.nl **
> http://www.BitWizard.nl/ ** +31-15-2600998 **
> *-- BitWizard writes Linux device drivers for any
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