| Message ID | 20191019210616.41199-1-jeffrey.l.hugo@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tty: serial: msm_serial: Fix flow control | expand |
On Sat 19 Oct 14:06 PDT 2019, Jeffrey Hugo wrote: > hci_qca interfaces to the wcn3990 via a uart_dm on the msm8998 mtp and > Lenovo Miix 630 laptop. As part of initializing the wcn3990, hci_qca > disables flow, configures the uart baudrate, and then reenables flow - at > which point an event is expected to be received over the uart from the > wcn3990. It is observed that this event comes after the baudrate change > but before hci_qca re-enables flow. This is unexpected, and is a result of > msm_reset() being broken. > > According to the uart_dm hardware documentation, it is recommended that > automatic hardware flow control be enabled by setting RX_RDY_CTL. Auto > hw flow control will manage RFR based on the configured watermark. When > there is space to receive data, the hw will assert RFR. When the watermark > is hit, the hw will de-assert RFR. > > The hardware documentation indicates that RFR can me manually managed via > CR when RX_RDY_CTL is not set. SET_RFR asserts RFR, and RESET_RFR > de-asserts RFR. > > msm_reset() is broken because after resetting the hardware, it > unconditionally asserts RFR via SET_RFR. This enables flow regardless of > the current configuration, and would undo a previous flow disable > operation. It should instead de-assert RFR via RESET_RFR to block flow > until the hardware is reconfigured. msm_serial should rely on the client > to specify that flow should be enabled, either via mctrl() or the termios > structure, and only assert RFR in response to those triggers. > I traced msm_reset() and msm_set_mctrl() and I get the following: swapper/0-1 [000] d..1 3.091726: msm_set_mctrl: msm_set_mctrl() reset rfr swapper/0-1 [000] d..1 3.117046: msm_set_mctrl: msm_set_mctrl() reset rfr swapper/0-1 [000] d..1 3.125484: msm_set_termios: msm_reset() set rfr swapper/0-1 [003] d..1 4.491430: msm_set_termios: msm_reset() set rfr swapper/0-1 [003] d..1 4.491733: msm_set_mctrl: msm_set_mctrl() auto rfr login-313 [001] d..1 78.010785: msm_set_mctrl: msm_set_mctrl() reset rfr login-313 [001] d..1 78.011007: msm_set_termios: msm_reset() set rfr login-313 [001] d..1 78.011021: msm_set_mctrl: msm_set_mctrl() auto rfr login-313 [001] d..1 78.063330: msm_set_termios: msm_reset() set rfr login-313 [001] d..1 78.063641: msm_set_termios: msm_reset() set rfr So while your change does make sense for BT, wouldn't this mean that with your patch and a 4-pin UART for the console I would end this dance with receive flow blocked? Regards, Bjorn > Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.") > Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com> > --- > drivers/tty/serial/msm_serial.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c > index 3657a24913fc..aedabf7646f1 100644 > --- a/drivers/tty/serial/msm_serial.c > +++ b/drivers/tty/serial/msm_serial.c > @@ -987,7 +987,7 @@ static void msm_reset(struct uart_port *port) > msm_write(port, UART_CR_CMD_RESET_ERR, UART_CR); > msm_write(port, UART_CR_CMD_RESET_BREAK_INT, UART_CR); > msm_write(port, UART_CR_CMD_RESET_CTS, UART_CR); > - msm_write(port, UART_CR_CMD_SET_RFR, UART_CR); > + msm_write(port, UART_CR_CMD_RESET_RFR, UART_CR); > > /* Disable DM modes */ > if (msm_port->is_uartdm) > -- > 2.17.1 >
On Sun, Oct 20, 2019 at 12:28 AM Bjorn Andersson <bjorn.andersson@linaro.org> wrote: > > On Sat 19 Oct 14:06 PDT 2019, Jeffrey Hugo wrote: > > > hci_qca interfaces to the wcn3990 via a uart_dm on the msm8998 mtp and > > Lenovo Miix 630 laptop. As part of initializing the wcn3990, hci_qca > > disables flow, configures the uart baudrate, and then reenables flow - at > > which point an event is expected to be received over the uart from the > > wcn3990. It is observed that this event comes after the baudrate change > > but before hci_qca re-enables flow. This is unexpected, and is a result of > > msm_reset() being broken. > > > > According to the uart_dm hardware documentation, it is recommended that > > automatic hardware flow control be enabled by setting RX_RDY_CTL. Auto > > hw flow control will manage RFR based on the configured watermark. When > > there is space to receive data, the hw will assert RFR. When the watermark > > is hit, the hw will de-assert RFR. > > > > The hardware documentation indicates that RFR can me manually managed via > > CR when RX_RDY_CTL is not set. SET_RFR asserts RFR, and RESET_RFR > > de-asserts RFR. > > > > msm_reset() is broken because after resetting the hardware, it > > unconditionally asserts RFR via SET_RFR. This enables flow regardless of > > the current configuration, and would undo a previous flow disable > > operation. It should instead de-assert RFR via RESET_RFR to block flow > > until the hardware is reconfigured. msm_serial should rely on the client > > to specify that flow should be enabled, either via mctrl() or the termios > > structure, and only assert RFR in response to those triggers. > > > > I traced msm_reset() and msm_set_mctrl() and I get the following: > swapper/0-1 [000] d..1 3.091726: msm_set_mctrl: msm_set_mctrl() reset rfr > swapper/0-1 [000] d..1 3.117046: msm_set_mctrl: msm_set_mctrl() reset rfr > swapper/0-1 [000] d..1 3.125484: msm_set_termios: msm_reset() set rfr > swapper/0-1 [003] d..1 4.491430: msm_set_termios: msm_reset() set rfr > swapper/0-1 [003] d..1 4.491733: msm_set_mctrl: msm_set_mctrl() auto rfr > login-313 [001] d..1 78.010785: msm_set_mctrl: msm_set_mctrl() reset rfr > login-313 [001] d..1 78.011007: msm_set_termios: msm_reset() set rfr > login-313 [001] d..1 78.011021: msm_set_mctrl: msm_set_mctrl() auto rfr > login-313 [001] d..1 78.063330: msm_set_termios: msm_reset() set rfr > login-313 [001] d..1 78.063641: msm_set_termios: msm_reset() set rfr > > So while your change does make sense for BT, wouldn't this mean that > with your patch and a 4-pin UART for the console I would end this dance > with receive flow blocked? No. I don't think it occurred to you to consider how RX_RDY_CTL factors into this. RX_RDY_CTL allows the hardware to enable flow when the hardware determines it is able to receive data. RX_RDY_CTL gets set in mctrl, and set_termios - essentially when the uart client has indicated flow can be enabled. Even though the console is a 2 wire console on msm8998, the driver will go through the same flow. I verified that RX_RDY_CTL is set on the console uart after boot, so we won't end up with flow blocked. However, this does bring up another issue. RX_RDY_CTL doesn't get unset in msm_reset. RESET_RX will disable the rx path in the hardware, and prevent RX_RDY_CTL from being active, but the rx path is enabled in set_baud_rate() before RX_RDY_CTL can be masked out in set_termios, so there may be a small window where flow can inadvertently enabled. I'll spin a v2 that also unsets RX_RDY_CTL in msm_reset(). > > Regards, > Bjorn > > > Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.") > > Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com> > > --- > > drivers/tty/serial/msm_serial.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c > > index 3657a24913fc..aedabf7646f1 100644 > > --- a/drivers/tty/serial/msm_serial.c > > +++ b/drivers/tty/serial/msm_serial.c > > @@ -987,7 +987,7 @@ static void msm_reset(struct uart_port *port) > > msm_write(port, UART_CR_CMD_RESET_ERR, UART_CR); > > msm_write(port, UART_CR_CMD_RESET_BREAK_INT, UART_CR); > > msm_write(port, UART_CR_CMD_RESET_CTS, UART_CR); > > - msm_write(port, UART_CR_CMD_SET_RFR, UART_CR); > > + msm_write(port, UART_CR_CMD_RESET_RFR, UART_CR); > > > > /* Disable DM modes */ > > if (msm_port->is_uartdm) > > -- > > 2.17.1 > >
On Mon 21 Oct 08:19 PDT 2019, Jeffrey Hugo wrote: > On Sun, Oct 20, 2019 at 12:28 AM Bjorn Andersson > <bjorn.andersson@linaro.org> wrote: > > > > On Sat 19 Oct 14:06 PDT 2019, Jeffrey Hugo wrote: > > > > > hci_qca interfaces to the wcn3990 via a uart_dm on the msm8998 mtp and > > > Lenovo Miix 630 laptop. As part of initializing the wcn3990, hci_qca > > > disables flow, configures the uart baudrate, and then reenables flow - at > > > which point an event is expected to be received over the uart from the > > > wcn3990. It is observed that this event comes after the baudrate change > > > but before hci_qca re-enables flow. This is unexpected, and is a result of > > > msm_reset() being broken. > > > > > > According to the uart_dm hardware documentation, it is recommended that > > > automatic hardware flow control be enabled by setting RX_RDY_CTL. Auto > > > hw flow control will manage RFR based on the configured watermark. When > > > there is space to receive data, the hw will assert RFR. When the watermark > > > is hit, the hw will de-assert RFR. > > > > > > The hardware documentation indicates that RFR can me manually managed via > > > CR when RX_RDY_CTL is not set. SET_RFR asserts RFR, and RESET_RFR > > > de-asserts RFR. > > > > > > msm_reset() is broken because after resetting the hardware, it > > > unconditionally asserts RFR via SET_RFR. This enables flow regardless of > > > the current configuration, and would undo a previous flow disable > > > operation. It should instead de-assert RFR via RESET_RFR to block flow > > > until the hardware is reconfigured. msm_serial should rely on the client > > > to specify that flow should be enabled, either via mctrl() or the termios > > > structure, and only assert RFR in response to those triggers. > > > > > > > I traced msm_reset() and msm_set_mctrl() and I get the following: > > swapper/0-1 [000] d..1 3.091726: msm_set_mctrl: msm_set_mctrl() reset rfr > > swapper/0-1 [000] d..1 3.117046: msm_set_mctrl: msm_set_mctrl() reset rfr > > swapper/0-1 [000] d..1 3.125484: msm_set_termios: msm_reset() set rfr > > swapper/0-1 [003] d..1 4.491430: msm_set_termios: msm_reset() set rfr > > swapper/0-1 [003] d..1 4.491733: msm_set_mctrl: msm_set_mctrl() auto rfr > > login-313 [001] d..1 78.010785: msm_set_mctrl: msm_set_mctrl() reset rfr > > login-313 [001] d..1 78.011007: msm_set_termios: msm_reset() set rfr > > login-313 [001] d..1 78.011021: msm_set_mctrl: msm_set_mctrl() auto rfr > > login-313 [001] d..1 78.063330: msm_set_termios: msm_reset() set rfr > > login-313 [001] d..1 78.063641: msm_set_termios: msm_reset() set rfr > > > > So while your change does make sense for BT, wouldn't this mean that > > with your patch and a 4-pin UART for the console I would end this dance > > with receive flow blocked? > > No. I don't think it occurred to you to consider how RX_RDY_CTL > factors into this. RX_RDY_CTL allows the hardware to enable flow when > the hardware determines it is able to receive data. RX_RDY_CTL gets > set in mctrl, and set_termios - essentially when the uart client has > indicated flow can be enabled. > I see, so per above trace when login does it's rfr toggling RX_RDY_CTL is already set (and will be maintained), so we'll allow flow at each part of the process. > Even though the console is a 2 wire console on msm8998, the driver > will go through the same flow. I verified that RX_RDY_CTL is set on > the console uart after boot, so we won't end up with flow blocked. > > However, this does bring up another issue. RX_RDY_CTL doesn't get > unset in msm_reset. RESET_RX will disable the rx path in the > hardware, and prevent RX_RDY_CTL from being active, but the rx path is > enabled in set_baud_rate() before RX_RDY_CTL can be masked out in > set_termios, so there may be a small window where flow can > inadvertently enabled. I'll spin a v2 that also unsets RX_RDY_CTL in > msm_reset(). > Yes, that sounds reasonable. And for the console case the difference will be that we deassert RFR while the serial is being reset and reconfigured; which sounds like the right thing to do. Regards, Bjorn > > > > Regards, > > Bjorn > > > > > Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.") > > > Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com> > > > --- > > > drivers/tty/serial/msm_serial.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c > > > index 3657a24913fc..aedabf7646f1 100644 > > > --- a/drivers/tty/serial/msm_serial.c > > > +++ b/drivers/tty/serial/msm_serial.c > > > @@ -987,7 +987,7 @@ static void msm_reset(struct uart_port *port) > > > msm_write(port, UART_CR_CMD_RESET_ERR, UART_CR); > > > msm_write(port, UART_CR_CMD_RESET_BREAK_INT, UART_CR); > > > msm_write(port, UART_CR_CMD_RESET_CTS, UART_CR); > > > - msm_write(port, UART_CR_CMD_SET_RFR, UART_CR); > > > + msm_write(port, UART_CR_CMD_RESET_RFR, UART_CR); > > > > > > /* Disable DM modes */ > > > if (msm_port->is_uartdm) > > > -- > > > 2.17.1 > > >
diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c index 3657a24913fc..aedabf7646f1 100644 --- a/drivers/tty/serial/msm_serial.c +++ b/drivers/tty/serial/msm_serial.c @@ -987,7 +987,7 @@ static void msm_reset(struct uart_port *port) msm_write(port, UART_CR_CMD_RESET_ERR, UART_CR); msm_write(port, UART_CR_CMD_RESET_BREAK_INT, UART_CR); msm_write(port, UART_CR_CMD_RESET_CTS, UART_CR); - msm_write(port, UART_CR_CMD_SET_RFR, UART_CR); + msm_write(port, UART_CR_CMD_RESET_RFR, UART_CR); /* Disable DM modes */ if (msm_port->is_uartdm)
hci_qca interfaces to the wcn3990 via a uart_dm on the msm8998 mtp and Lenovo Miix 630 laptop. As part of initializing the wcn3990, hci_qca disables flow, configures the uart baudrate, and then reenables flow - at which point an event is expected to be received over the uart from the wcn3990. It is observed that this event comes after the baudrate change but before hci_qca re-enables flow. This is unexpected, and is a result of msm_reset() being broken. According to the uart_dm hardware documentation, it is recommended that automatic hardware flow control be enabled by setting RX_RDY_CTL. Auto hw flow control will manage RFR based on the configured watermark. When there is space to receive data, the hw will assert RFR. When the watermark is hit, the hw will de-assert RFR. The hardware documentation indicates that RFR can me manually managed via CR when RX_RDY_CTL is not set. SET_RFR asserts RFR, and RESET_RFR de-asserts RFR. msm_reset() is broken because after resetting the hardware, it unconditionally asserts RFR via SET_RFR. This enables flow regardless of the current configuration, and would undo a previous flow disable operation. It should instead de-assert RFR via RESET_RFR to block flow until the hardware is reconfigured. msm_serial should rely on the client to specify that flow should be enabled, either via mctrl() or the termios structure, and only assert RFR in response to those triggers. Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.") Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com> --- drivers/tty/serial/msm_serial.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)