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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 4B9DAC433E1 for ; Sun, 17 May 2020 15:04:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3401C2070A for ; Sun, 17 May 2020 15:04:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728048AbgEQPEm convert rfc822-to-8bit (ORCPT ); Sun, 17 May 2020 11:04:42 -0400 Received: from gloria.sntech.de ([185.11.138.130]:43306 "EHLO gloria.sntech.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727970AbgEQPEl (ORCPT ); Sun, 17 May 2020 11:04:41 -0400 Received: from ip5f5aa64a.dynamic.kabel-deutschland.de ([95.90.166.74] helo=diego.localnet) by gloria.sntech.de with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jaKq5-00017L-6e; Sun, 17 May 2020 17:04:29 +0200 From: Heiko =?ISO-8859-1?Q?St=FCbner?= To: Giulio Benetti Cc: gregkh@linuxfoundation.org, jslaby@suse.com, andriy.shevchenko@linux.intel.com, matwey.kornilov@gmail.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, lukas@wunner.de, christoph.muellner@theobroma-systems.com Subject: Re: [PATCH v2 4/7] serial: 8250: Handle implementations not having TEMT interrupt using em485 Date: Sun, 17 May 2020 17:04:28 +0200 Message-ID: <3036126.9QgpAzkLCg@diego> In-Reply-To: References: <20200325231422.1502366-1-heiko@sntech.de> <12195570.sTQbgxCmNy@diego> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Giulio, Am Donnerstag, 26. März 2020, 03:02:39 CEST schrieb Giulio Benetti: > Il 26/03/2020 01:05, Heiko Stübner ha scritto: > > Am Donnerstag, 26. März 2020, 00:47:38 CET schrieb Giulio Benetti: > >> very cleaner way to handle TEMT as a capability! > >> And I've found one thing... > >> > >> Il 26/03/2020 00:14, Heiko Stuebner ha scritto: > >>> From: Giulio Benetti > >>> > >>> Some 8250 ports have a TEMT interrupt but it's not a part of the 8250 > >>> standard, instead only available on some implementations. > >>> > >>> The current em485 implementation does not work on ports without it. > >>> The only chance to make it work is to loop-read on LSR register. > >>> > >>> So add UART_CAP_TEMT to mark 8250 uarts having this interrupt, > >>> update all current em485 users with that capability and make > >>> the stop_tx function loop-read on uarts not having it. > >>> > >>> Signed-off-by: Giulio Benetti > >>> [moved to use added UART_CAP_TEMT, use readx_poll_timeout] > >>> Signed-off-by: Heiko Stuebner > >>> --- > >>> drivers/tty/serial/8250/8250.h | 1 + > >>> drivers/tty/serial/8250/8250_bcm2835aux.c | 2 +- > >>> drivers/tty/serial/8250/8250_of.c | 2 ++ > >>> drivers/tty/serial/8250/8250_omap.c | 2 +- > >>> drivers/tty/serial/8250/8250_port.c | 25 +++++++++++++++++++---- > >>> 5 files changed, 26 insertions(+), 6 deletions(-) > >>> > >>> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h > >>> index 52bb21205bb6..770eb00db497 100644 > >>> --- a/drivers/tty/serial/8250/8250.h > >>> +++ b/drivers/tty/serial/8250/8250.h > >>> @@ -82,6 +82,7 @@ struct serial8250_config { > >>> #define UART_CAP_MINI (1 << 17) /* Mini UART on BCM283X family lacks: > >>> * STOP PARITY EPAR SPAR WLEN5 WLEN6 > >>> */ > >>> +#define UART_CAP_TEMT (1 << 18) /* UART has TEMT interrupt */ > >>> > >>> #define UART_BUG_QUOT (1 << 0) /* UART has buggy quot LSB */ > >>> #define UART_BUG_TXEN (1 << 1) /* UART has buggy TX IIR status */ > >>> diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c > >>> index 12d03e678295..3881242424ca 100644 > >>> --- a/drivers/tty/serial/8250/8250_bcm2835aux.c > >>> +++ b/drivers/tty/serial/8250/8250_bcm2835aux.c > >>> @@ -91,7 +91,7 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev) > >>> return -ENOMEM; > >>> > >>> /* initialize data */ > >>> - up.capabilities = UART_CAP_FIFO | UART_CAP_MINI; > >>> + up.capabilities = UART_CAP_FIFO | UART_CAP_MINI | UART_CAP_TEMT; > >>> up.port.dev = &pdev->dev; > >>> up.port.regshift = 2; > >>> up.port.type = PORT_16550; > >>> diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c > >>> index 65e9045dafe6..841f6fcb2878 100644 > >>> --- a/drivers/tty/serial/8250/8250_of.c > >>> +++ b/drivers/tty/serial/8250/8250_of.c > >>> @@ -225,6 +225,8 @@ static int of_platform_serial_probe(struct platform_device *ofdev) > >>> &port8250.overrun_backoff_time_ms) != 0) > >>> port8250.overrun_backoff_time_ms = 0; > >>> > >>> + port8250.capabilities |= UART_CAP_TEMT; > >>> + > >> > >> Shouldn't this be NOT UART_CAP_TEMT set by default? On all other > >> vendor specific files you enable it, I think here you shouldn't enable > >> it too by default. Right? > > > > 8250_of does use the em485 emulation - see of_platform_serial_setup() > > So I did go by the lazy assumption that any 8250 driver using rs485 > > before my series always used the interrupt driver code path, so > > implicitly required to have the TEMT interrupt. > > > > Of course, you're right that with the 8250_of maybe not all variants > > actually do have this interrupt, so falling back to the polling here might > > be safer. > > Probably here it's worth introducing a dt boolean property like > "temt-capability", then you set or not UART_CAP_TEMT according to its > presence in dts. This way all cases are covered and we can act > completely through dts files. > > What about that? Sorry that this was sitting around for over a month. I think there are two problems with this: (1) this would break backwards compatibility ... right now the whole code just assumes that everyone does support the TEMT interrupt, so adding a property to keep it working would break old DTs, which is something that should not happen ... I guess one option would be to use the inverse no-temt-interrupt (2) uarts handled by 8250_of are still identified by their compatible though and there is no generic 8250-of compatible, so the presence / absence of the temt capability should actually just be bound to the relevant compatible. So my "gut feeling" is to just keep the current way (was expecting temt-capability before anyway) until an uart variant without temt comes along Heiko