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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 251ACC433EF for ; Tue, 1 Feb 2022 17:45:59 +0000 (UTC) Received: from localhost ([::1]:45724 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nExE5-0003cv-RK for qemu-devel@archiver.kernel.org; Tue, 01 Feb 2022 12:45:57 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59162) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nEvS3-0004tZ-4q for qemu-devel@nongnu.org; Tue, 01 Feb 2022 10:52:15 -0500 Received: from mail08.asahi-net.or.jp ([202.224.55.48]:58193) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nEvS1-0001Vx-6q for qemu-devel@nongnu.org; Tue, 01 Feb 2022 10:52:14 -0500 Received: from sakura.ysato.name (ik1-413-38519.vs.sakura.ne.jp [153.127.30.23]) (Authenticated sender: PQ4Y-STU) by mail08.asahi-net.or.jp (Postfix) with ESMTPA id 2554920C0A; Wed, 2 Feb 2022 00:52:08 +0900 (JST) Received: from localhost.ysato.ml (b150065.dynamic.ppp.asahi-net.or.jp [202.213.150.65]) by sakura.ysato.name (Postfix) with ESMTPSA id 4BD221C00DA; Wed, 2 Feb 2022 00:52:08 +0900 (JST) Date: Wed, 02 Feb 2022 00:52:03 +0900 Message-ID: From: Yoshinori Sato To: Thomas Huth Subject: Re: [PATCH 1/2] hw/char/renesas_sci: Add fifo buffer to backend interface. In-Reply-To: References: <20220131094246.772550-1-ysato@users.sourceforge.jp> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?ISO-8859-4?Q?Goj=F2?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.2 (arm-unknown-linux-androideabi) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Received-SPF: softfail client-ip=202.224.55.48; envelope-from=ysato@users.sourceforge.jp; helo=mail08.asahi-net.or.jp X-Spam_score_int: -11 X-Spam_score: -1.2 X-Spam_bar: - X-Spam_report: (-1.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?ISO-8859-1?Q?Marc-Andr=E9?= Lureau , Paolo Bonzini , Magnus Damm , qemu-devel@nongnu.org, Philippe =?ISO-8859-1?Q?Mathieu-Daud=E9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 01 Feb 2022 15:48:58 +0900, Thomas Huth wrote: > > On 31/01/2022 10.42, Yoshinori Sato wrote: > > SCI does not have a fifo, it is necessary to send and receive > > at a bit rate speed. > > But, qemu's chardev backend does not have a buffer, > > so it sends received data continuously. > > By buffering the received data with the FIFO, continuous > > received data can be received. > > Hi! > > If you describe it like this, it sounds like you're now emulating a > buffer that is not there with real hardware? Is that really what you > want here, i.e. wouldn't this hide problems with the real hardware > that are mitigated in QEMU with this buffer? There is no such buffer in the real hardware. It's not possible with real hardware, but the chardev backend passes data faster than the bitrate. There is no problem if the received data is supplied at the timing when it can be received, but since it is difficult to match the timing accurately, we expect that the buffer will absorb the difference in timing. > Anyway, please use scripts/get_maintainer.pl to get a list of people > who should be put on CC:, otherwise your patches might get lost in the > high traffic of the mailing list. OK. > > Thomas > > -- Yoshinori Sato