From mboxrd@z Thu Jan 1 00:00:00 1970 From: Balakrishna Godavarthi Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate change command Date: Wed, 23 Jan 2019 18:27:42 +0530 Message-ID: References: <20190111013707.GD261387@google.com> <194b5d18ea86830b6a24939d483a964c@codeaurora.org> <20190111235633.GK261387@google.com> <20190115234628.GQ261387@google.com> <20190117160944.GV3691@localhost> <20190117172109.GU261387@google.com> <20190118094416.GB3691@localhost> <20190119003109.GD261387@google.com> <24831204bab89250099ca56e7562bd16@codeaurora.org> <20190122215330.GI261387@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190122215330.GI261387@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Matthias Kaehlcke 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 Hi Matthias, On 2019-01-23 03:23, Matthias Kaehlcke wrote: > On Mon, Jan 21, 2019 at 08:11:39PM +0530, Balakrishna Godavarthi wrote: >> Hi Matthias, >> >> On 2019-01-19 06:01, Matthias Kaehlcke wrote: >> > On Fri, Jan 18, 2019 at 10:44:16AM +0100, Johan Hovold wrote: >> > > On Thu, Jan 17, 2019 at 09:21:09AM -0800, Matthias Kaehlcke wrote: >> > > >> > > > I observed that the qcom_geni_serial driver doesn't raise RTS with >> > > > flow control disabled. It seems we have to investigate why that's the >> > > > case. I agree that the driver should be platform agnostic. >> > > >> > > Sounds like a driver bug, unless the hardware is just "odd". The >> > > driver implementation of this looks very non-standard judging from a >> > > quick peek. >> > > >> > > In fact, qcom_geni_serial_get_mctrl() is currently a no-op if hardware >> > > flow control is not enabled: >> > > >> > > if (uart_console(uport) || !uart_cts_enabled(uport)) >> > > return; >> > > >> > > Perhaps dropping the !uart_cts_enabled() test is sufficient. >> > >> > Thanks for taking a look Johan, that was indeed the problem (also >> > in set_mctrl()). I posted a fix: >> > https://lore.kernel.org/patchwork/patch/1033611/ >> > >> > Balakrishna, the following (applied on top of your patch) works for me >> > with the UART patch above: >> > >> >> [Bala]: will test and update BT patch accordingly. > > Note that Johan pointed out that hci_uart_set_flow_control() deasserts > RTS when flow control is disabled, so the _set_rts() calls can be > removed. With that only a single action needs to be undone in case of > an error, you can consider to keep the return instead of using the > goto introduced by my patch. > [Bala]: ok sure. will note this. > Please keep/adapt the "Deassert RTS while changing the baudrate ..." > comment to leave it clear to posterity why flow control is disabled > during baudrate changes. It's fairly obvious once you understand the > problem and that disabling flow control deasserts RTS, but it took us > a while to get there, initially we only had a comment saying > "disabling flow control is mandatory" (I recall I inquired about this > multiple times during the initial review of the wcn3990 patches ;-) > > Thanks > > Matthias -- Regards Balakrishna.