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=-8.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 CA52BC433DB for ; Mon, 8 Feb 2021 10:35:17 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 6BF5064E54 for ; Mon, 8 Feb 2021 10:35:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6BF5064E54 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=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:Subject:To:From: Date:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=nxp6PpO6rWHH+hn+Js0TsFEbNf0efnIBTFchs6wqTNA=; b=uxRa4JDz5I9nLnllNkf5ISD4z C1MkvaqwpIdz9J3ZVz66DiRANXofzEc24wmPFHZmr5Ocp8VsB8yDhmHzb6kepM28jqLqX5uy09Phj tZTiloJnQRTUVsiGBQtmGFLSUnEZgKBoEHpV9rDd/WKJwDjRc+v+TcEcurvq7YxujaBeN8r0u0tUw +Ycd0WoSzIWiw1PNIZOJYTQWEeCtuD+L/e8QB3tb1nATriW/PEw+/mo+r7XMKt+CwjQ7aXGlHb7YP wmu5J4htjBn0GjMxgIjFnC//JHohBPvDTCdJ5oAMJ8Kl1Jom8twzMOt2yD28FsXhKhyivMNLNkSAC XB8K6Ti+g==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l93ry-0007pq-CA; Mon, 08 Feb 2021 10:34:14 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l93rv-0007pF-3Q for linux-arm-kernel@lists.infradead.org; Mon, 08 Feb 2021 10:34:12 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5159D64E56; Mon, 8 Feb 2021 10:34:10 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1l93rr-00Ckco-KX; Mon, 08 Feb 2021 10:34:08 +0000 MIME-Version: 1.0 Date: Mon, 08 Feb 2021 10:34:07 +0000 From: Marc Zyngier To: Hector Martin 'marcan' Subject: Re: [PATCH 05/18] tty: serial: samsung_tty: add support for Apple UARTs In-Reply-To: References: <20210204203951.52105-1-marcan@marcan.st> <20210204203951.52105-6-marcan@marcan.st> <87lfc1l4lo.wl-maz@kernel.org> User-Agent: Roundcube Webmail/1.4.10 Message-ID: <73116feaa00de9173d1f2c35ce16e08f@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: marcan@marcan.st, soc@kernel.org, linux-arm-kernel@lists.infradead.org, robh+dt@kernel.org, arnd@kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, olof@lixom.net X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210208_053411_340598_0EF5D402 X-CRM114-Status: GOOD ( 21.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Cc: Arnd Bergmann , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, soc@kernel.org, robh+dt@kernel.org, Olof Johansson , linux-arm-kernel@lists.infradead.org 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 2021-02-07 09:12, Hector Martin 'marcan' wrote: > On 06/02/2021 22.15, Marc Zyngier wrote: [...] >>> - spin_lock_irqsave(&port->lock, flags); >>> + /* Only lock if called from IRQ context */ >>> + if (irq != NO_IRQ) >>> + spin_lock_irqsave(&port->lock, flags); >> >> Isn't that actually dangerous? What prevents the interrupt from firing >> right in the middle of this sequence and create havoc when called from >> enable_tx_pio()? I fail to see what you gain with sidestepping the >> locking. > > The callpath here is: > > uart_start -> __uart_start -> (uart_ops.start_tx) > s3c24xx_serial_start_tx -> s3c24xx_serial_start_tx_pio -> > enable_tx_pio -> s3c24xx_serial_tx_chars > > And uart_start takes the uart_port lock. None of the serial functions > take the lock because the serial core already does, but obviously the > IRQ handler needs to, *if* it's called as an IRQ handler only. Right, that's the part I missed, thanks for pointing this out. It'd probably be cleaner to move the whole s3c24xx_serial_tx_chars() into a helper and keep the locking in the interrupt handler proper. [...] >>> diff --git a/include/uapi/linux/serial_core.h >>> b/include/uapi/linux/serial_core.h >>> index 62c22045fe65..59d102b674db 100644 >>> --- a/include/uapi/linux/serial_core.h >>> +++ b/include/uapi/linux/serial_core.h >>> @@ -277,4 +277,7 @@ >>> /* Freescale LINFlexD UART */ >>> #define PORT_LINFLEXUART 122 >>> +/* Apple Silicon (M1/T8103) UART (Samsung variant) */ >>> +#define PORT_APPLE 123 >>> + >> >> Do you actually need a new port type here? Looking at the driver >> itself, it is mainly used to work out the IRQ model. Maybe introducing >> a new irq_type field in the port structure would be better than >> exposing this to userspace (which should see something that is exactly >> the same as a S3C UART). > > Well... every S3C variant already has its own port type here. > > #define PORT_S3C2410 55 > #define PORT_S3C2440 61 > #define PORT_S3C2400 67 > #define PORT_S3C2412 73 > #define PORT_S3C6400 84 > > If we don't introduce a new one, which one should we pretend to be? :) Pick one! :D > I agree that it might make sense to merge all of these into one, > though; I don't know what the original reason for splitting them out > is. But now that they're part of the userspace API, this might not be > a good idea. Though, unsurprisingly, some googling suggests there are > zero users of these defines in userspace. I don't think we can do that, but I don't think we should keep adding to this unless there is a very good reason. Greg would know, I expect. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel