From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B113C43387 for ; Fri, 11 Jan 2019 01:37:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CBBF2133F for ; Fri, 11 Jan 2019 01:37:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="aVLWml4X" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729373AbfAKBhJ (ORCPT ); Thu, 10 Jan 2019 20:37:09 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:33357 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728988AbfAKBhJ (ORCPT ); Thu, 10 Jan 2019 20:37:09 -0500 Received: by mail-pl1-f194.google.com with SMTP id z23so6019743plo.0 for ; Thu, 10 Jan 2019 17:37:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=6q/xuJNr3sBokRPwM7RLrMqV7Gur7gMpsOwsUuBthOg=; b=aVLWml4XKnApFgE2Q8PtpPD/DlQNKQrKrNsHisKzt8pYhhhOTzn81GWo1lzA7h+A78 KiEMjzMxh2ENr5rHRRPM0ZD0scmKSA9mX27lBst0k54bw9P54NmKNpl/BHxMWUyW7Ra2 27pFF0tAgTgNs1fMrnbUpGUM/YcfgI6omo228= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=6q/xuJNr3sBokRPwM7RLrMqV7Gur7gMpsOwsUuBthOg=; b=QOHG5VDshEcmfUuGb4OXjqVs0FhWuRmOy4yE66x3jhbGs7TdNfFBLN7aWAnyWFr2dJ ImPrEDN7vd+2PryjQR1RXhCXA3/VaAjTGO4QchzX0573f81TDb8eLjWXhrlkW8a2WG8D bn3CAERiuifO7aKqU735ZRxCn73Gzxmbzn/gfKx/Y43OCXK6oTRlC7tKVxo2GzYyKTVO 8iFXn8ylalDd4VsnhyqlD/MGrVKOYL6nirN/AIjOSNMlk5qA5mMf9jtb9asincHVcUz+ LeKy1lzkz+qcqURTxYiTXOEWXbJzCL/MTJWkN+Yfv6o5Q2oGWMXDxqkQogF+VeQ9uOtM xRMQ== X-Gm-Message-State: AJcUukdGUNjVUjetdC4Q/SBu4qEyFzyI1c+jwQdBGgFydClS082MwklC PsG2p5aDN8SC9URyQK3w7+g9Sw== X-Google-Smtp-Source: ALg8bN4tw0O29N8dG2GqX8fmXJOiKGYbbzqFIdaODZZGVrvW3VYOb1baZENAWKIxOn3FxZhlopy5tQ== X-Received: by 2002:a17:902:e290:: with SMTP id cf16mr12947722plb.81.1547170628474; Thu, 10 Jan 2019 17:37:08 -0800 (PST) Received: from localhost ([2620:15c:202:1:75a:3f6e:21d:9374]) by smtp.gmail.com with ESMTPSA id d80sm216447471pfm.146.2019.01.10.17.37.07 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 10 Jan 2019 17:37:07 -0800 (PST) Date: Thu, 10 Jan 2019 17:37:07 -0800 From: Matthias Kaehlcke 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 Subject: Re: [PATCH v5 2/5] Bluetooth: hci_qca: Deassert RTS while baudrate change command 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 Content-Disposition: inline In-Reply-To: <61301df80bd6a8ee0265b31b7f6a3aa1@codeaurora.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-bluetooth-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-bluetooth@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