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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBC13C433F5 for ; Thu, 10 Feb 2022 10:46:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240064AbiBJKqS (ORCPT ); Thu, 10 Feb 2022 05:46:18 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:55788 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231878AbiBJKqO (ORCPT ); Thu, 10 Feb 2022 05:46:14 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E63EEFF1; Thu, 10 Feb 2022 02:46:14 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 93EF3B824B3; Thu, 10 Feb 2022 10:46:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAAC8C004E1; Thu, 10 Feb 2022 10:46:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1644489972; bh=qhgOSNqzVwAgQEC+/Ughopou3AgvMKYhrHTrwnUjWFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W4iUUfliBgRfgMb3+LAgt77ybKOcO8zcmnMp7YXwwzY8e2ldIwu+gZuQj4SyOCk0m +u+WSqYFt+URKQQUJQ1v2flcaSrGHdy0TGgBwv5T6kfaMXo8mWFH2lGxzVf+JtE+xc hLd/K/qM8dR02Z4k3bRl+LKOlbGx1P/hhKDs/bGg= Date: Thu, 10 Feb 2022 11:46:09 +0100 From: Greg Kroah-Hartman To: Zev Weiss Cc: Joel Stanley , Andrew Jeffery , Jiri Slaby , Andy Shevchenko , Konstantin Aladyshev , Oskar Senft , openbmc@lists.ozlabs.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type Message-ID: References: <20220209203414.23491-1-zev@bewilderbeest.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 10, 2022 at 01:22:09AM -0800, Zev Weiss wrote: > On Thu, Feb 10, 2022 at 12:20:12AM PST, Greg Kroah-Hartman wrote: > > On Wed, Feb 09, 2022 at 11:49:47PM -0800, Zev Weiss wrote: > > > On Wed, Feb 09, 2022 at 11:40:42PM PST, Greg Kroah-Hartman wrote: > > > > On Wed, Feb 09, 2022 at 12:34:14PM -0800, Zev Weiss wrote: > > > > > Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to > > > > > set up register mapping") fixed a bug that had, as a side-effect, > > > > > prevented the 8250_aspeed_vuart driver from enabling the VUART's > > > > > FIFOs. However, fixing that (and hence enabling the FIFOs) has in > > > > > turn revealed what appears to be a hardware bug in the ASPEED VUART in > > > > > which the host-side THRE bit doesn't get if the BMC-side receive FIFO > > > > > trigger level is set to anything but one byte. This causes problems > > > > > for polled-mode writes from the host -- for example, Linux kernel > > > > > console writes proceed at a glacial pace (less than 100 bytes per > > > > > second) because the write path waits for a 10ms timeout to expire > > > > > after every character instead of being able to continue on to the next > > > > > character upon seeing THRE asserted. (GRUB behaves similarly.) > > > > > > > > > > As a workaround, introduce a new port type for the ASPEED VUART that's > > > > > identical to PORT_16550A as it had previously been using, but with > > > > > UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to > > > > > one byte, which (experimentally) seems to avoid the problematic THRE > > > > > behavior. > > > > > > > > > > Signed-off-by: Zev Weiss > > > > > Tested-by: Konstantin Aladyshev > > > > > > > > Do we need a "Fixes:" tag here as well? > > > > > > I was wondering the same -- I left it out because it didn't seem like it was > > > strictly a bug in the earlier commit that's really being fixed per se, but > > > perhaps that's an overly pedantic distinction. I can certainly add it if > > > you'd prefer. > > > > This obviously fixes an issue, if you don't have a specific commit that > > caused it, a cc: stable@vger.kernel.org should be added so we know to > > backport this to all stable kernels. > > > > Okay -- well, I suppose it's a fix in the sense that if you have the earlier > commit, you'll also want this one, so I'll add the tag. Please do. > > > > > --- > > > > > drivers/tty/serial/8250/8250_aspeed_vuart.c | 2 +- > > > > > drivers/tty/serial/8250/8250_port.c | 8 ++++++++ > > > > > include/uapi/linux/serial_core.h | 3 +++ > > > > > 3 files changed, 12 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > index 2350fb3bb5e4..c2cecc6f47db 100644 > > > > > --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > @@ -487,7 +487,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) > > > > > port.port.irq = irq_of_parse_and_map(np, 0); > > > > > port.port.handle_irq = aspeed_vuart_handle_irq; > > > > > port.port.iotype = UPIO_MEM; > > > > > - port.port.type = PORT_16550A; > > > > > + port.port.type = PORT_ASPEED_VUART; > > > > > port.port.uartclk = clk; > > > > > port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP > > > > > | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST; > > > > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > > > > > index 3b12bfc1ed67..973870ebff69 100644 > > > > > --- a/drivers/tty/serial/8250/8250_port.c > > > > > +++ b/drivers/tty/serial/8250/8250_port.c > > > > > @@ -307,6 +307,14 @@ static const struct serial8250_config uart_config[] = { > > > > > .rxtrig_bytes = {1, 32, 64, 112}, > > > > > .flags = UART_CAP_FIFO | UART_CAP_SLEEP, > > > > > }, > > > > > + [PORT_ASPEED_VUART] = { > > > > > + .name = "ASPEED VUART", > > > > > + .fifo_size = 16, > > > > > + .tx_loadsz = 16, > > > > > + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00, > > > > > + .rxtrig_bytes = {1, 4, 8, 14}, > > > > > + .flags = UART_CAP_FIFO, > > > > > + }, > > > > > }; > > > > > > > > > > /* Uart divisor latch read */ > > > > > diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h > > > > > index c4042dcfdc0c..cd11748833e6 100644 > > > > > --- a/include/uapi/linux/serial_core.h > > > > > +++ b/include/uapi/linux/serial_core.h > > > > > @@ -274,4 +274,7 @@ > > > > > /* Freescale LINFlexD UART */ > > > > > #define PORT_LINFLEXUART 122 > > > > > > > > > > +/* ASPEED AST2x00 virtual UART */ > > > > > +#define PORT_ASPEED_VUART 123 > > > > > > > > Why does this value have to be in a uapi header file? What userspace > > > > tool is going to need this? > > > > > > > > > > I only put it there because that was where all the other port type constants > > > were defined, and wondered the same thing about the lot of them. Is there a > > > userspace tool that makes use of any of these? > > > > Not really, please don't add it if you do not require it. > > > > It seems like an odd inconsistency to put this one particular definition > somewhere else when the other 100+ of its siblings are in the uapi header; > would you want a preceding patch to move them all somewhere under > include/linux? (Which in turn doesn't really seem like a change for -stable > I'd think.) > > Though actually, on further investigation I see those constants are in fact > exposed to userspace in struct serial_struct->type (via > TIOCGSERIAL/TIOCSSERIAL), and via the 'type' sysfs attribute, so I'd think > we'd probably want to keep them as they are? One of these days I'll unwind this mess. There should not be any need to export this to userspace as userspace doesn't really care about it. but for now, sure, keep it :( thanks, greg k-h 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.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (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 46FB6C433F5 for ; Thu, 10 Feb 2022 10:47:04 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4JvYN62jsdz3c7S for ; Thu, 10 Feb 2022 21:47:02 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=W4iUUfli; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linuxfoundation.org (client-ip=2604:1380:4601:e00::1; helo=ams.source.kernel.org; envelope-from=gregkh@linuxfoundation.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=W4iUUfli; dkim-atps=neutral Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4JvYMG6Bbqz3bPK; Thu, 10 Feb 2022 21:46:17 +1100 (AEDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7C1E2B824A5; Thu, 10 Feb 2022 10:46:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAAC8C004E1; Thu, 10 Feb 2022 10:46:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1644489972; bh=qhgOSNqzVwAgQEC+/Ughopou3AgvMKYhrHTrwnUjWFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W4iUUfliBgRfgMb3+LAgt77ybKOcO8zcmnMp7YXwwzY8e2ldIwu+gZuQj4SyOCk0m +u+WSqYFt+URKQQUJQ1v2flcaSrGHdy0TGgBwv5T6kfaMXo8mWFH2lGxzVf+JtE+xc hLd/K/qM8dR02Z4k3bRl+LKOlbGx1P/hhKDs/bGg= Date: Thu, 10 Feb 2022 11:46:09 +0100 From: Greg Kroah-Hartman To: Zev Weiss Subject: Re: [PATCH] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type Message-ID: References: <20220209203414.23491-1-zev@bewilderbeest.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: openbmc@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development list for OpenBMC List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-aspeed@lists.ozlabs.org, Konstantin Aladyshev , Andrew Jeffery , openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org, Oskar Senft , linux-serial@vger.kernel.org, Andy Shevchenko , Jiri Slaby , linux-arm-kernel@lists.infradead.org Errors-To: openbmc-bounces+openbmc=archiver.kernel.org@lists.ozlabs.org Sender: "openbmc" On Thu, Feb 10, 2022 at 01:22:09AM -0800, Zev Weiss wrote: > On Thu, Feb 10, 2022 at 12:20:12AM PST, Greg Kroah-Hartman wrote: > > On Wed, Feb 09, 2022 at 11:49:47PM -0800, Zev Weiss wrote: > > > On Wed, Feb 09, 2022 at 11:40:42PM PST, Greg Kroah-Hartman wrote: > > > > On Wed, Feb 09, 2022 at 12:34:14PM -0800, Zev Weiss wrote: > > > > > Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to > > > > > set up register mapping") fixed a bug that had, as a side-effect, > > > > > prevented the 8250_aspeed_vuart driver from enabling the VUART's > > > > > FIFOs. However, fixing that (and hence enabling the FIFOs) has in > > > > > turn revealed what appears to be a hardware bug in the ASPEED VUART in > > > > > which the host-side THRE bit doesn't get if the BMC-side receive FIFO > > > > > trigger level is set to anything but one byte. This causes problems > > > > > for polled-mode writes from the host -- for example, Linux kernel > > > > > console writes proceed at a glacial pace (less than 100 bytes per > > > > > second) because the write path waits for a 10ms timeout to expire > > > > > after every character instead of being able to continue on to the next > > > > > character upon seeing THRE asserted. (GRUB behaves similarly.) > > > > > > > > > > As a workaround, introduce a new port type for the ASPEED VUART that's > > > > > identical to PORT_16550A as it had previously been using, but with > > > > > UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to > > > > > one byte, which (experimentally) seems to avoid the problematic THRE > > > > > behavior. > > > > > > > > > > Signed-off-by: Zev Weiss > > > > > Tested-by: Konstantin Aladyshev > > > > > > > > Do we need a "Fixes:" tag here as well? > > > > > > I was wondering the same -- I left it out because it didn't seem like it was > > > strictly a bug in the earlier commit that's really being fixed per se, but > > > perhaps that's an overly pedantic distinction. I can certainly add it if > > > you'd prefer. > > > > This obviously fixes an issue, if you don't have a specific commit that > > caused it, a cc: stable@vger.kernel.org should be added so we know to > > backport this to all stable kernels. > > > > Okay -- well, I suppose it's a fix in the sense that if you have the earlier > commit, you'll also want this one, so I'll add the tag. Please do. > > > > > --- > > > > > drivers/tty/serial/8250/8250_aspeed_vuart.c | 2 +- > > > > > drivers/tty/serial/8250/8250_port.c | 8 ++++++++ > > > > > include/uapi/linux/serial_core.h | 3 +++ > > > > > 3 files changed, 12 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > index 2350fb3bb5e4..c2cecc6f47db 100644 > > > > > --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > @@ -487,7 +487,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) > > > > > port.port.irq = irq_of_parse_and_map(np, 0); > > > > > port.port.handle_irq = aspeed_vuart_handle_irq; > > > > > port.port.iotype = UPIO_MEM; > > > > > - port.port.type = PORT_16550A; > > > > > + port.port.type = PORT_ASPEED_VUART; > > > > > port.port.uartclk = clk; > > > > > port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP > > > > > | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST; > > > > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > > > > > index 3b12bfc1ed67..973870ebff69 100644 > > > > > --- a/drivers/tty/serial/8250/8250_port.c > > > > > +++ b/drivers/tty/serial/8250/8250_port.c > > > > > @@ -307,6 +307,14 @@ static const struct serial8250_config uart_config[] = { > > > > > .rxtrig_bytes = {1, 32, 64, 112}, > > > > > .flags = UART_CAP_FIFO | UART_CAP_SLEEP, > > > > > }, > > > > > + [PORT_ASPEED_VUART] = { > > > > > + .name = "ASPEED VUART", > > > > > + .fifo_size = 16, > > > > > + .tx_loadsz = 16, > > > > > + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00, > > > > > + .rxtrig_bytes = {1, 4, 8, 14}, > > > > > + .flags = UART_CAP_FIFO, > > > > > + }, > > > > > }; > > > > > > > > > > /* Uart divisor latch read */ > > > > > diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h > > > > > index c4042dcfdc0c..cd11748833e6 100644 > > > > > --- a/include/uapi/linux/serial_core.h > > > > > +++ b/include/uapi/linux/serial_core.h > > > > > @@ -274,4 +274,7 @@ > > > > > /* Freescale LINFlexD UART */ > > > > > #define PORT_LINFLEXUART 122 > > > > > > > > > > +/* ASPEED AST2x00 virtual UART */ > > > > > +#define PORT_ASPEED_VUART 123 > > > > > > > > Why does this value have to be in a uapi header file? What userspace > > > > tool is going to need this? > > > > > > > > > > I only put it there because that was where all the other port type constants > > > were defined, and wondered the same thing about the lot of them. Is there a > > > userspace tool that makes use of any of these? > > > > Not really, please don't add it if you do not require it. > > > > It seems like an odd inconsistency to put this one particular definition > somewhere else when the other 100+ of its siblings are in the uapi header; > would you want a preceding patch to move them all somewhere under > include/linux? (Which in turn doesn't really seem like a change for -stable > I'd think.) > > Though actually, on further investigation I see those constants are in fact > exposed to userspace in struct serial_struct->type (via > TIOCGSERIAL/TIOCSSERIAL), and via the 'type' sysfs attribute, so I'd think > we'd probably want to keep them as they are? One of these days I'll unwind this mess. There should not be any need to export this to userspace as userspace doesn't really care about it. but for now, sure, keep it :( thanks, greg k-h 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 E8BBEC433F5 for ; Thu, 10 Feb 2022 10:47:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=djSBzsZU48449Q5OZ6+8b8H9NdNDhhtWevgiOcm8LFY=; b=Q61W4bqYdB6EM8 5XwWsvvXkKOO5rA0n4yhEz459Bfbyh+nyhYCiaqnES8cQJElvky5MJuZnady10+x5KU5wmYmUArNC TEx2Gjn4X8pDCJ2FJi5a5K3Zhq5QZG91ot+VCyYZU/vYvvhCjLRHgCYVZ+Zq+bPx2vtF17wJkxdSC +s1EUOOiXwrReS1NpxiO2keC8at5l/1zmhljH+1GOAYz8ZTevYiQ+3Lp7aO8Vb0piGyTnTr9eC5Xi AlL1V2XQClWgWM2uESRuw8b9dn7CCkH5b7HvM5TX9HcbmX2dPBNBI+uQt8eqwovlvEpYTsfMddj/K Hca5++iRIDhkvAH1x1zA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nI6xv-003Uja-Er; Thu, 10 Feb 2022 10:46:19 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nI6xq-003Uig-Sl for linux-arm-kernel@lists.infradead.org; Thu, 10 Feb 2022 10:46:16 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7C1E2B824A5; Thu, 10 Feb 2022 10:46:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAAC8C004E1; Thu, 10 Feb 2022 10:46:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1644489972; bh=qhgOSNqzVwAgQEC+/Ughopou3AgvMKYhrHTrwnUjWFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=W4iUUfliBgRfgMb3+LAgt77ybKOcO8zcmnMp7YXwwzY8e2ldIwu+gZuQj4SyOCk0m +u+WSqYFt+URKQQUJQ1v2flcaSrGHdy0TGgBwv5T6kfaMXo8mWFH2lGxzVf+JtE+xc hLd/K/qM8dR02Z4k3bRl+LKOlbGx1P/hhKDs/bGg= Date: Thu, 10 Feb 2022 11:46:09 +0100 From: Greg Kroah-Hartman To: Zev Weiss Cc: Joel Stanley , Andrew Jeffery , Jiri Slaby , Andy Shevchenko , Konstantin Aladyshev , Oskar Senft , openbmc@lists.ozlabs.org, linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] serial: 8250_aspeed_vuart: add PORT_ASPEED_VUART port type Message-ID: References: <20220209203414.23491-1-zev@bewilderbeest.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220210_024615_265007_FD898B1C X-CRM114-Status: GOOD ( 52.37 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Feb 10, 2022 at 01:22:09AM -0800, Zev Weiss wrote: > On Thu, Feb 10, 2022 at 12:20:12AM PST, Greg Kroah-Hartman wrote: > > On Wed, Feb 09, 2022 at 11:49:47PM -0800, Zev Weiss wrote: > > > On Wed, Feb 09, 2022 at 11:40:42PM PST, Greg Kroah-Hartman wrote: > > > > On Wed, Feb 09, 2022 at 12:34:14PM -0800, Zev Weiss wrote: > > > > > Commit 54da3e381c2b ("serial: 8250_aspeed_vuart: use UPF_IOREMAP to > > > > > set up register mapping") fixed a bug that had, as a side-effect, > > > > > prevented the 8250_aspeed_vuart driver from enabling the VUART's > > > > > FIFOs. However, fixing that (and hence enabling the FIFOs) has in > > > > > turn revealed what appears to be a hardware bug in the ASPEED VUART in > > > > > which the host-side THRE bit doesn't get if the BMC-side receive FIFO > > > > > trigger level is set to anything but one byte. This causes problems > > > > > for polled-mode writes from the host -- for example, Linux kernel > > > > > console writes proceed at a glacial pace (less than 100 bytes per > > > > > second) because the write path waits for a 10ms timeout to expire > > > > > after every character instead of being able to continue on to the next > > > > > character upon seeing THRE asserted. (GRUB behaves similarly.) > > > > > > > > > > As a workaround, introduce a new port type for the ASPEED VUART that's > > > > > identical to PORT_16550A as it had previously been using, but with > > > > > UART_FCR_R_TRIG_00 instead to set the receive FIFO trigger level to > > > > > one byte, which (experimentally) seems to avoid the problematic THRE > > > > > behavior. > > > > > > > > > > Signed-off-by: Zev Weiss > > > > > Tested-by: Konstantin Aladyshev > > > > > > > > Do we need a "Fixes:" tag here as well? > > > > > > I was wondering the same -- I left it out because it didn't seem like it was > > > strictly a bug in the earlier commit that's really being fixed per se, but > > > perhaps that's an overly pedantic distinction. I can certainly add it if > > > you'd prefer. > > > > This obviously fixes an issue, if you don't have a specific commit that > > caused it, a cc: stable@vger.kernel.org should be added so we know to > > backport this to all stable kernels. > > > > Okay -- well, I suppose it's a fix in the sense that if you have the earlier > commit, you'll also want this one, so I'll add the tag. Please do. > > > > > --- > > > > > drivers/tty/serial/8250/8250_aspeed_vuart.c | 2 +- > > > > > drivers/tty/serial/8250/8250_port.c | 8 ++++++++ > > > > > include/uapi/linux/serial_core.h | 3 +++ > > > > > 3 files changed, 12 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > index 2350fb3bb5e4..c2cecc6f47db 100644 > > > > > --- a/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > +++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c > > > > > @@ -487,7 +487,7 @@ static int aspeed_vuart_probe(struct platform_device *pdev) > > > > > port.port.irq = irq_of_parse_and_map(np, 0); > > > > > port.port.handle_irq = aspeed_vuart_handle_irq; > > > > > port.port.iotype = UPIO_MEM; > > > > > - port.port.type = PORT_16550A; > > > > > + port.port.type = PORT_ASPEED_VUART; > > > > > port.port.uartclk = clk; > > > > > port.port.flags = UPF_SHARE_IRQ | UPF_BOOT_AUTOCONF | UPF_IOREMAP > > > > > | UPF_FIXED_PORT | UPF_FIXED_TYPE | UPF_NO_THRE_TEST; > > > > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > > > > > index 3b12bfc1ed67..973870ebff69 100644 > > > > > --- a/drivers/tty/serial/8250/8250_port.c > > > > > +++ b/drivers/tty/serial/8250/8250_port.c > > > > > @@ -307,6 +307,14 @@ static const struct serial8250_config uart_config[] = { > > > > > .rxtrig_bytes = {1, 32, 64, 112}, > > > > > .flags = UART_CAP_FIFO | UART_CAP_SLEEP, > > > > > }, > > > > > + [PORT_ASPEED_VUART] = { > > > > > + .name = "ASPEED VUART", > > > > > + .fifo_size = 16, > > > > > + .tx_loadsz = 16, > > > > > + .fcr = UART_FCR_ENABLE_FIFO | UART_FCR_R_TRIG_00, > > > > > + .rxtrig_bytes = {1, 4, 8, 14}, > > > > > + .flags = UART_CAP_FIFO, > > > > > + }, > > > > > }; > > > > > > > > > > /* Uart divisor latch read */ > > > > > diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h > > > > > index c4042dcfdc0c..cd11748833e6 100644 > > > > > --- a/include/uapi/linux/serial_core.h > > > > > +++ b/include/uapi/linux/serial_core.h > > > > > @@ -274,4 +274,7 @@ > > > > > /* Freescale LINFlexD UART */ > > > > > #define PORT_LINFLEXUART 122 > > > > > > > > > > +/* ASPEED AST2x00 virtual UART */ > > > > > +#define PORT_ASPEED_VUART 123 > > > > > > > > Why does this value have to be in a uapi header file? What userspace > > > > tool is going to need this? > > > > > > > > > > I only put it there because that was where all the other port type constants > > > were defined, and wondered the same thing about the lot of them. Is there a > > > userspace tool that makes use of any of these? > > > > Not really, please don't add it if you do not require it. > > > > It seems like an odd inconsistency to put this one particular definition > somewhere else when the other 100+ of its siblings are in the uapi header; > would you want a preceding patch to move them all somewhere under > include/linux? (Which in turn doesn't really seem like a change for -stable > I'd think.) > > Though actually, on further investigation I see those constants are in fact > exposed to userspace in struct serial_struct->type (via > TIOCGSERIAL/TIOCSSERIAL), and via the 'type' sysfs attribute, so I'd think > we'd probably want to keep them as they are? One of these days I'll unwind this mess. There should not be any need to export this to userspace as userspace doesn't really care about it. but for now, sure, keep it :( thanks, greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel