Re: [PATCH] Powerpc 8xx CPM_UART delay in receive

Le 14/08/2012 16:52, Alan Cox a écrit :

On Tue, 14 Aug 2012 16:26:28 +0200
Christophe Leroy [off-list ref] wrote:

quoted

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