On Thu, Feb 14, 2008 at 07:55:44PM +1030, David Newall wrote: > The current 2.6 driver maintains it's own buffer. I think that's a bad > thing: usbserial already buffers writes, and the extra buffer copy seems > unnecessary, however it does solve the putchar problem. Buffered (i.e. > by the 2.6 series pl2303 driver) data is written as soon as practicable, > regardless of CTS/DTR. The same general workaround, but placed in > pl2303_send seems correct to me; that is, stop submitting write urbs > when the remote end lowers CTS/DTR, and trigger the resume from the > interrupt callback (specifically in update_line_status.)
Where does the usbserial core buffer writes on 2.6? The serial_write() function just passes the data straight down to the usb-serial child driver directly, no copying or buffering happens that I can see. > To make it clear: Even aside from the buffer in 2.6's pl2303.c, there's > a race: An in-flight write URB can fill all hardware buffers, making > unsafe what previously appeared to be a safe write. I think it's > essential to delay submission of the URB on a stop-transmit condition. It's up to the individual driver to know when their buffers are filled up. The big problem is, a lot of these cheap usb-serial devices (like the pl2303) don't have a way to report the uart queue filled-state back to the host, so things can easily get over-run as you have found out. If you really want to use a usb-serial device in an environment where such kinds of flow control are essential, then you have to buy the more expensive ones. The I/O networks devices handle this kind of thing very well, and have done so since the 2.3 days, but they cost much more than the cheap pl2303-based devices. thanks, greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
