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[104.188.17.28]) by smtp.gmail.com with ESMTPSA id o64sm24649254pjb.24.2019.10.19.23.28.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Oct 2019 23:28:19 -0700 (PDT) Date: Sat, 19 Oct 2019 23:28:16 -0700 From: Bjorn Andersson To: Jeffrey Hugo Cc: agross@kernel.org, gregkh@linuxfoundation.org, jslaby@suse.com, linux-arm-msm@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] tty: serial: msm_serial: Fix flow control Message-ID: <20191020062816.GE1669@tuxbook-pro> References: <20191019210616.41199-1-jeffrey.l.hugo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191019210616.41199-1-jeffrey.l.hugo@gmail.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org 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 > --- > 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 >