On Tue, Mar 16, 2010 at 5:05 PM, Jason Wessel <jason.wessel@xxxxxxxxxxxxx> wrote: > I aggregated and ported all usb patches I have previously posted which > are not mainlined into a single series aimed at providing a stable usb > console. Jason, are you aware that the FTDI chips correctly signals the RTS/CTS lines when it is busy doing USB processing? They work ok ignoring RTS/CTS up to about 600Kb/s. For higher baud rates you needs to implement RTS/CTS. My embedded system has a DMA based serial port that I am running at 2Mb/s. The RTS/CTS handshake works to automatically flow control the hardware DMA system. If you don't do this the chip will simply drop the characters. > > Greg Kroah-Hartman already picked up the first 2 patches in the > series, but for completeness they are provided here because one of the > other patches requires the context changes. > > Differences in V2 vs V1 patch set > * The optimize usb sysrq was dropped entirely > * Removed the unused export symbol per Alan Stern's comments > * Updated the definition of usb_poll_irq() per Alan Stern's comments > > > Thanks, > Jason. > > > -- The recap about synchronous usb serial consoles -- > > This is picking up where Alan Stern and I left off after a discussion > in September 2009. > > The serial uart code implements the console writes synchronously such > that you get the data right away and "pay the toll" in terms of system > performance loss if you do lots of printk's to the console. The usb > serial console code just eats the data if there is no room left in the > queue, and you do not see the data until the interrupts are restored. > > If we assume the main reason you would use a usb console device is to > get printk's then every effort should be made to be able to see the > printk's on the usb console device. In this patch series, two > conditions must be met before the hcd device would get polled. > > 1) The data write is a usb serial console write > 2) The usb serial driver has set the variable max_in_flight_urbs > > Based on Alan's comments about the 1ms minimum response time for the > hcd device I ended up using a maximum 3ms delay loop. The 3ms was > selected based on testing the usb_debug device and the ftdi usb rs232 > port. I found the usb_debug device needed the 1ms and the ftdi device > required slightly more than 2ms in the worst case else there was some > sporadic data loss. > > I also tested incurring the penalty 3ms for each write with the device > in a "failed" capacity. In that case it introduced a 3ms delay for > each printk() which only showed any noticeable delay with the "SysRq t" > packet. > > Part of having the console stable requires that usb sysrq handler get > executed in a tasklet. The hcd device lock is always held while the > driver call backs are executed. The means you cannot get the sysrq > printk's out to the usb console device after the in_flight urb queue > is filled. > > Thanks, > Jason. > > --- > > The following changes since commit a3d3203e4bb40f253b1541e310dc0f9305be7c84: > Linus Torvalds (1): > Merge branch 'release' of git://git.kernel.org/.../lenb/linux-acpi-2.6 > > are available in the git repository at: > > git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/linux-2.6-kgdb.git for_gregkh > > Jason Wessel (5): > tty_port,usb-console: Fix usb serial console open/close regression > usb-serial: Use tty_port version of console instead of the usb_serial_port version > usb-console: pass baud from console to the initial tty open > usb-hcd,usb-console: poll hcd device to force usb console writes > usb-serialy,sysrq: Run the sysrq handler in a tasklet > > drivers/char/sysrq.c | 29 ++++++++++++++++ > drivers/char/tty_port.c | 2 +- > drivers/usb/core/hcd.c | 10 +++++ > drivers/usb/serial/console.c | 70 ++++++++++++++++++++++---------------- > drivers/usb/serial/ftdi_sio.c | 9 +++-- > drivers/usb/serial/generic.c | 6 ++-- > drivers/usb/serial/pl2303.c | 8 +++-- > drivers/usb/serial/usb-serial.c | 4 +- > drivers/usb/serial/usb_debug.c | 2 +- > include/linux/sysrq.h | 4 ++ > include/linux/tty.h | 1 + > include/linux/usb.h | 3 ++ > include/linux/usb/serial.h | 2 - > 13 files changed, 104 insertions(+), 46 deletions(-) > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- Jon Smirl jonsmirl@xxxxxxxxx -- 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
