From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Kaehlcke Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate change command Date: Thu, 10 Jan 2019 17:37:07 -0800 Message-ID: <20190111013707.GD261387@google.com> References: <20181220144639.15928-1-bgodavar@codeaurora.org> <20181220144639.15928-3-bgodavar@codeaurora.org> <20190109145224.GN14782@localhost> <20190110143928.GE3430@localhost> <61301df80bd6a8ee0265b31b7f6a3aa1@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <61301df80bd6a8ee0265b31b7f6a3aa1@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Balakrishna Godavarthi Cc: Johan Hovold , marcel@holtmann.org, johan.hedberg@gmail.com, linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org, hemantg@codeaurora.org, linux-arm-msm@vger.kernel.org, Johan Hovold List-Id: linux-arm-msm@vger.kernel.org On Thu, Jan 10, 2019 at 08:22:12PM +0530, Balakrishna Godavarthi wrote: > Hi Johan, > > On 2019-01-10 20:09, Johan Hovold wrote: > > On Thu, Jan 10, 2019 at 08:04:12PM +0530, Balakrishna Godavarthi wrote: > > > Hi Johan, > > > > > > On 2019-01-09 20:22, Johan Hovold wrote: > > > > On Thu, Dec 20, 2018 at 08:16:36PM +0530, Balakrishna Godavarthi wrote: > > > >> This patch will help to stop frame reassembly errors while changing > > > >> the baudrate. This is because host send a change baudrate request > > > >> command to the chip with 115200 bps, Whereas chip will change their > > > >> UART clocks to the enable for new baudrate and sends the response > > > >> for the change request command with newer baudrate, On host side > > > >> we are still operating in 115200 bps which results of reading garbage > > > >> data. Here we are pulling RTS line, so that chip we will wait to send > > > >> data > > > >> to host until host change its baudrate. > > > > > >> + /* Deassert RTS while changing the baudrate of chip and host. > > > >> + * This will prevent chip from transmitting its response with > > > >> + * the new baudrate while the host port is still operating at > > > >> + * the old speed. > > > >> + */ > > > >> + qcadev = serdev_device_get_drvdata(hu->serdev); > > > >> + if (qcadev->btsoc_type == QCA_WCN3990) > > > >> + serdev_device_set_rts(hu->serdev, false); > > > >> + > > > > > > > > This may not do what you want unless you also disable hardware flow > > > > control. > > > > > Here my requirement here is to block the chip to send its data before > > > HOST changes it is baudrate. So if i disable flow control lines of > > > HOST which will be in low state. so that the chip will send it data > > > before HOST change the baudrate of HOST. which results in frame > > > reassembly error. > > > > Not sure I understand what you're trying to say above. My point is that > > you cannot reliable control RTS when you have automatic flow control > > enabled (i.e. it is managed by hardware and it's state reflects whether > > there's room in the UART receive FIFO). > > > > Johan > > [Bala]: Yes i got your point, but our driver I suppose with "our driver" you refer to a Qualcomm UART driver like qcom_geni_serial.c. Unless the Bluetooth controller is really tied to some specific SoC (e.g. because it is on-chip) you shouldn't make assumptions about the UART driver or hardware beyond standard behavior. But even if we assume that the driver you mention is used, I think you are rather confirming Johan's concern than dispersing it: > will not support automatic flow control (based on the FIFO status) > unless we explicitly enabled via software. i.e. if we enable the > flow, hardware will look for it else it will not looks for CTS or > RTS Line. So we agree that the UART hardware may change RTS if hardware flow control is enabled? static int qca_send_power_pulse(struct hci_uart *hu, u8 cmd) { ... hci_uart_set_flow_control(hu, false); ... } I still find it utterly confusing that set_flow_control(false) enables flow control, but that's what it does, hence after qca_send_power_pulse() flow control is (re-)enabled. So far I haven't seen problems with qcom_geni_serial.c overriding the level set with serdev_device_set_rts(), but I tend to agree with Johan that this could be a problem (if not with this UART (driver) then with another). I'm not keen about adding more flow control on/off clutter, but if that is needed for the driver to operate reliably across platforms so be it. Cheers Matthias