Le 14/08/2012 16:52, Alan Cox a écrit :
On Tue, 14 Aug 2012 16:26:28 +0200
Christophe Leroy <christophe.leroy@xxxxxx> wrote:
Hello,
I'm not sure who to address this Patch to either
It fixes a delay issue with CPM UART driver on Powerpc MPC8xx.
The problem is that with the actual code, the driver waits 32 IDLE patterns before returning the received data to the upper level. It means for instance about 1 second at 300 bauds.
This fix limits to one byte the waiting period.
Take a look how the 8250 does it - I think you want to set the value
based upon the data rate. Your patch will break it for everyone doing
high seed I/O.
Alan
I'm not sure I understand what you mean. As far as I can see 8250/16550
is working a bit different, as it is based on a fifo and triggers an
interrupt as soon as a given number of bytes is received. I also see
that in case this amount is not reached, there is a receive-timeout
which goes on after no byte is received for a duration of more than 4 bytes.
The PowerPC CPM is working differently. It doesn't use a fifo but
buffers. Buffers are handed to the microprocessor only when they are
full or after a timeout period which is adjustable. In the driver, the
buffers are configured with a size of 32 bytes. And the timeout is set
to the size of the buffer. That is this timeout that I'm reducing to 1
byte in my proposed patch. I can't see what it would break for high
speed I/O.
Christophe
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