On Thu, Oct 03, 2024 at 11:29:58AM -0700, Doug Anderson wrote:
On Tue, Oct 1, 2024 at 5:51 AM Johan Hovold johan+linaro@kernel.org wrote:
The receiver should not be enabled until the port is opened so drop the bogus call to start rx from the setup code which is shared with the console implementation.
This was added for some confused implementation of hibernation support, but the receiver must not be started unconditionally as the port may not have been open when hibernating the system.
Could you provide a motivation for your patch in the description? Is patch needed for something (perhaps a future patch in the series)? Is it fixing a bug? Does it save power? Is the call harmless but cleaner to get rid of?
I was trying to bring some order to this driver so that the receiver is enabled when the port is opened and disabled when it is closed again as expected, and get rid of the random calls added in places where they do not belong (e.g., as Bjorn also mentioned, why was the call to start rx added in the port setup code if it was needed for hibernation?).
Data "received" over the wire before opening the port should not be processed, but it also turns out that enabling the receiver before the port is opened can confuse the firmware and break the "stale" rx timer handling so that data is only forwarded in chunks of 12 bytes instead of when each char is received.
Fixes: 35781d8356a2 ("tty: serial: qcom-geni-serial: Add support for Hibernation feature") Cc: stable@vger.kernel.org # 6.2 Cc: Aniket Randive quic_arandive@quicinc.com Signed-off-by: Johan Hovold johan+linaro@kernel.org
drivers/tty/serial/qcom_geni_serial.c | 1 - 1 file changed, 1 deletion(-)
diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index 6f0db310cf69..9ea6bd09e665 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -1152,7 +1152,6 @@ static int qcom_geni_serial_port_setup(struct uart_port *uport) false, true, true); geni_se_init(&port->se, UART_RX_WM, port->rx_fifo_depth - 2); geni_se_select_mode(&port->se, port->dev_data->mode);
qcom_geni_serial_start_rx(uport);FWIW, I found at least one thing that's broken by your patch. If you enable kgdb (but _not_ "kgdboc_earlycon") and then add "kgdbwait" to the kernel command line parameters then things will be broken after your patch. You'll drop into the debugger but can't interact with it. The "kgdboc_earlycon" path handles this because of "qcom_geni_serial_enable_early_read()" but it doesn't seem like there's anything that handles it for normal kgdb. If you drop in the debugger later it'll probably work if you've got an "agetty" running because that'll enable the RX path.
Ok, so the kgdb has started relying on this call since d8851a96ba25 ("tty: serial: qcom-geni-serial: Add a poll_init() function"). Thanks for pointing that out.
The polled console code should not be calling the port setup code unconditionally anyway so I'll fix this up as well in v3.
Johan