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[85.230.190.116]) by smtp.gmail.com with ESMTPSA id w16-v6sm314749ljw.11.2019.01.17.08.09.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Jan 2019 08:09:43 -0800 (PST) Received: from johan by xi.terra with local (Exim 4.91) (envelope-from ) id 1gkAEi-0007fy-Be; Thu, 17 Jan 2019 17:09:45 +0100 Date: Thu, 17 Jan 2019 17:09:44 +0100 From: Johan Hovold To: Matthias Kaehlcke Cc: Balakrishna Godavarthi , 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 Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate change command Message-ID: <20190117160944.GV3691@localhost> References: <20181220144639.15928-3-bgodavar@codeaurora.org> <20190109145224.GN14782@localhost> <20190110143928.GE3430@localhost> <61301df80bd6a8ee0265b31b7f6a3aa1@codeaurora.org> <20190111013707.GD261387@google.com> <194b5d18ea86830b6a24939d483a964c@codeaurora.org> <20190111235633.GK261387@google.com> <20190115234628.GQ261387@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190115234628.GQ261387@google.com> User-Agent: Mutt/1.11.2 (2019-01-07) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 15, 2019 at 03:46:28PM -0800, Matthias Kaehlcke wrote: > Using RTS seems|ed like a nice solutions, since it's the native way to > prevent the controller from sending data, instead of doing some custom > hack. However Johan seems to be fairly convinced that flow control and > manual toggling of RTS can be problematic, and we have seen that > disabling flow control has its own problems. Maybe it's time to > consider other solutions like the DISCARD_RX flag we discussed > earlier. Not that I really liked this custom solution, but in the end > it might be a more robust way to address the issue. > > Johan/Marcel/others: Do you have any further ideas or input on this? I don't see why deasserting RTS wouldn't work, well at least as long as the RTS signal is wired correctly. My point was simply that calling serdev_device_set_rts() will generally not work unless you first disable automatic (i.e. hw-managed) flow control using serdev_device_set_flow_control(). The exact behaviour is serial-controller dependent, but I assume the driver needs to be platform agnostic. Johan