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=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 80001C433ED for ; Wed, 19 May 2021 06:12:55 +0000 (UTC) Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0A669611AD for ; Wed, 19 May 2021 06:12:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A669611AD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=desiato.20200630; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:Cc:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=kH8T+Gyef3OB+FN3uX8lsEMPiSwuCcU3WLC+siuVi0A=; b=IfvgsSsOAZRKoDtUNBSgcZtDR bWyTg3z+tr19hb5ihLp2rMTCEsId2JuMs1ovc+gub5wAIFlJXwX3DR7lsmquAeW7EJI6Bto/w4yLb XZUlF+f7Nl5d3+i9eng3+oolX02cIx1lgM2X/LXsohyngGidChTnoRMnnkafNzOHyt94TJ+pQpyKf XjIvTp0veiZpo3stKHJLBIFEYj0y2reds56fPA3SlP+KgjkIBtidXrVZYPMoqRT+BpzHljI6RDJ3J zHgVP/JKSjFxk5ICNTT1mfe/5o1Vohak3axiQJEtJPZeYQhtlZqKhPK/70CqOaL8WGcQWsZL78x5n DVlOY2Ewg==; Received: from localhost ([::1] helo=desiato.infradead.org) by desiato.infradead.org with esmtp (Exim 4.94 #2 (Red Hat Linux)) id 1ljFQE-002xB8-R5; Wed, 19 May 2021 06:11:11 +0000 Received: from bombadil.infradead.org ([2607:7c80:54:e::133]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1ljFQB-002xAh-1d for linux-arm-kernel@desiato.infradead.org; Wed, 19 May 2021 06:11:07 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To: Subject:Sender:Reply-To:Content-ID:Content-Description; bh=E0IobIzQGFKtYjnVLAhsERrEFaAtOpKnjVXmJUrJllo=; b=QPyAG+FtgK4tkQC7Rp16AWkp0N c3odRsqYT2FJ/TkgkO725/RN1JxSgAXyxYc3msu7aC/tNrVB2oBaTkox9o7oUHn3FfjehFFrj0qha I+ExBREt9loVnV1PolI8abSHfcfsXD2Nkm7npInFTIepePPzGeOa61MnkfQKQmrGC1uYDcUEYcVs0 JmiuEksu/dpLaS/MljNwzWxz7fHyOGKLvTS3f0tL9GNw0pSnYKEuJqCWvomY8XdSFnymkrqlLnnzw q8UxfzsezwlD/+4Lwf8Beqa6akk0GFj5mEonZBBHFx7noPZbwpajXuHhacahMgQ4cKTu86KHekjsY bcTD+HWg==; Received: from mail-wr1-f52.google.com ([209.85.221.52]) by bombadil.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1ljFQ8-00FAlk-AY for linux-arm-kernel@lists.infradead.org; Wed, 19 May 2021 06:11:05 +0000 Received: by mail-wr1-f52.google.com with SMTP id a4so12662953wrr.2 for ; Tue, 18 May 2021 23:11:01 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=E0IobIzQGFKtYjnVLAhsERrEFaAtOpKnjVXmJUrJllo=; b=AgPE0K+uIh5hUJBgUOugvqSimiFcO3ByhPj19gffYpAr1A6ERz408g68YY7Y89XGRX fi1AkA4TgMIUfPCqLHH4jW9wTzOUOgRNsnGNY2IYLYeZXRb7AqC3Noxe3bk3Ol8O8CDJ e7dkfjhb/8TUlNKC7DcEdOZO6IHAOaPvax3U/4V4M0ywn/nCAXt4yIa0vBaFBk9uizgL NlUoNZ2OYgqErCEYTynhBNoeEZ7E4S5PlRyjv14ClrDVgl2CopNkqu9hXWoEkFi4FTl1 RjnrjT7tJ8ci5FkwY0AP1+1rdSp22/bvcGPuCN54jZCecwLjK+tDvFLA0IRW3I4svYTP suiQ== X-Gm-Message-State: AOAM532XTUXyJoYLA1sUHKS8lETeFHcWgS0YRNzcpaZ60VIRfAK7e+zL Kjmqqkb30TOEISAamDCS3gmxQ5/3wko= X-Google-Smtp-Source: ABdhPJwIim9jf63DzBY3rwRC398B+hBCfBG7+Rs9X9JQQtLHoS1CD+Yq0iLOe0Ctgxg5qXG/UsNQ8A== X-Received: by 2002:adf:f3cc:: with SMTP id g12mr12461094wrp.300.1621404660316; Tue, 18 May 2021 23:11:00 -0700 (PDT) Received: from ?IPv6:2a0b:e7c0:0:107::70f? ([2a0b:e7c0:0:107::70f]) by smtp.gmail.com with ESMTPSA id m10sm24644065wrr.2.2021.05.18.23.10.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 May 2021 23:10:59 -0700 (PDT) Subject: Re: [PATCH v2 1/2] serial: 8250: Add UART_BUG_TXRACE workaround for Aspeed VUART To: Andrew Jeffery , linux-serial@vger.kernel.org Cc: gregkh@linuxfoundation.org, joel@jms.id.au, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, openbmc@lists.ozlabs.org, jenmin_yuan@aspeedtech.com, ryan_chen@aspeedtech.com, miltonm@us.ibm.com, ChiaWei Wang References: <20210519000704.3661773-1-andrew@aj.id.au> <20210519000704.3661773-2-andrew@aj.id.au> From: Jiri Slaby Message-ID: <8c14289a-9e81-f8de-b451-664a72ea5963@kernel.org> Date: Wed, 19 May 2021 08:10:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210519000704.3661773-2-andrew@aj.id.au> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210518_231104_406818_1BB61BCF X-CRM114-Status: GOOD ( 30.56 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 19. 05. 21, 2:07, Andrew Jeffery wrote: > Aspeed Virtual UARTs directly bridge e.g. the system console UART on the > LPC bus to the UART interface on the BMC's internal APB. As such there's > no RS-232 signalling involved - the UART interfaces on each bus are > directly connected as the producers and consumers of the one set of > FIFOs. > > The APB in the AST2600 generally runs at 100MHz while the LPC bus peaks > at 33MHz. The difference in clock speeds exposes a race in the VUART > design where a Tx data burst on the APB interface can result in a byte > lost on the LPC interface. The symptom is LSR[DR] remains clear on the > LPC interface despite data being present in its Rx FIFO, while LSR[THRE] > remains clear on the APB interface as the host has not consumed the data > the BMC has transmitted. In this state, the UART has stalled and no > further data can be transmitted without manual intervention (e.g. > resetting the FIFOs, resulting in loss of data). > > The recommended work-around is to insert a read cycle on the APB > interface between writes to THR. > > Cc: ChiaWei Wang > Signed-off-by: Andrew Jeffery > --- > drivers/tty/serial/8250/8250.h | 1 + > drivers/tty/serial/8250/8250_aspeed_vuart.c | 1 + > drivers/tty/serial/8250/8250_port.c | 10 ++++++++++ > 3 files changed, 12 insertions(+) > > diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h > index 52bb21205bb6..34aa2714f3c9 100644 > --- a/drivers/tty/serial/8250/8250.h > +++ b/drivers/tty/serial/8250/8250.h > @@ -88,6 +88,7 @@ struct serial8250_config { > #define UART_BUG_NOMSR (1 << 2) /* UART has buggy MSR status bits (Au1x00) */ > #define UART_BUG_THRE (1 << 3) /* UART has buggy THRE reassertion */ > #define UART_BUG_PARITY (1 << 4) /* UART mishandles parity if FIFO enabled */ > +#define UART_BUG_TXRACE (1 << 5) /* UART Tx fails to set remote DR */ > > > #ifdef CONFIG_SERIAL_8250_SHARE_IRQ > diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c > index a28a394ba32a..4caab8714e2c 100644 > --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c > +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c > @@ -440,6 +440,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) > port.port.status = UPSTAT_SYNC_FIFO; > port.port.dev = &pdev->dev; > port.port.has_sysrq = IS_ENABLED(CONFIG_SERIAL_8250_CONSOLE); > + port.bugs |= UART_BUG_TXRACE; > > rc = sysfs_create_group(&vuart->dev->kobj, &aspeed_vuart_attr_group); > if (rc < 0) > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index d45dab1ab316..9d44b2b2ff18 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -1809,6 +1809,16 @@ void serial8250_tx_chars(struct uart_8250_port *up) > count = up->tx_loadsz; > do { > serial_out(up, UART_TX, xmit->buf[xmit->tail]); > + if (up->bugs & UART_BUG_TXRACE) { > + /* The Aspeed BMC virtual UARTs have a bug where data This is not how a multiline comment should start. It should have been: /* * The Aspeed BMC virtual... > + * may get stuck in the BMC's Tx FIFO from bursts of > + * writes on the APB interface. > + * > + * Delay back-to-back writes by a read cycle to avoid > + * stalling the VUART. > + */ > + (void)serial_in(up, UART_SCR); (void) is useless here. It's only syntactic sugar which wouldn't even filter out a warning about unused result (if serial_in was marked w/ __must_check/warn_unused_result attribute). > + } > xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1); > port->icount.tx++; > if (uart_circ_empty(xmit)) > thanks, -- js suse labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel