Hello > I could make write_room return the ACTUAL fill-level information of >the device. Now, the tty layer would potentially hand over more bytes to >generic_write that it can handle. This would result in only a part of the >data been but to URBs and sent off to the device. > I would a assume that the tty layer would just issue another write_room, > learn that there is still room available on the device, and then try to > sent the remaining bytes via a another generic_write. As now at least some > of the URBs are already recycled, it can sent off more data to the device. I gave it a shot. My basic assumption was wrong -- the tty layer apparently relies on write_room returning the number of bytes that a subsequent write will transfer. If write_room returns more bytes that write will actually take, characters will be swallowed. Here in detail what happens : [the write function can transfer 640 bytes max, i.e. a pool of 10 URBs with 64 bytes payload each] [the buffer of the serial device can take up to 4096 bytes -- this is what write_room returns] write_room(): 4096 bytes free write(bytes=1095) write -- sent=640 bytes -- remaining=455 bytes [now the tty layer tries to transfer the remaining bytes. It remains unsuccessful until the transmission of at least 1 URBs has finished, and it is recycled. The bytes in between 2 successful calls to write ,i.e. #bytes sent != 0, are swallowed] write_room(): 4096 bytes free write(bytes=1) write -- sent=0 bytes write_room(): 4096 bytes free write(bytes=454) write -- sent=0 bytes write_room(): 4096 bytes free write(bytes=1) write -- sent=0 bytes write_room(): 4096 bytes free write(bytes=453) write -- sent=0 bytes ... usbrsa_write_callback() -- URB #0 freed usbrsa_write_callback() -- URB #1 freed write_room(): 4096 bytes free [ 34 bytes swallowed] write(bytes=421) write -- sent=128 bytes -- remaining=293 bytes write_room(): 4096 bytes free write(bytes=1) write -- sent=0 bytes write_room(): 4096 bytes free write(bytes=292) write -- sent=0 bytes .... -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
