Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S933956AbdC3OOt (ORCPT <rfc822;w@1wt.eu>);
        Thu, 30 Mar 2017 10:14:49 -0400
Received: from imap.thunk.org ([74.207.234.97]:40316 "EHLO imap.thunk.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S933107AbdC3OOn (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 30 Mar 2017 10:14:43 -0400
Date: Thu, 30 Mar 2017 10:11:53 -0400
From: "Theodore Ts'o" <tytso@mit.edu>
To: Olliver Schinagl <oliver@schinagl.nl>
Cc: Vignesh R <vigneshr@ti.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Laxman Dewangan <ldewangan@nvidia.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Alexandre Courbot <gnurou@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        "dev@linux-sunxi.org" <dev@linux-sunxi.org>,
        Ed Blake <ed.blake@imgtec.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexander Sverdlin <alexander.sverdlin@nokia.com>,
        Yegor Yefremov <yegorslists@googlemail.com>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Heiko Stuebner <heiko@sntech.de>, Jason Uy <jason.uy@broadcom.com>,
        Douglas Anderson <dianders@chromium.org>,
        Peter Hurley <peter@hurleysoftware.com>,
        Tony Lindgren <tony@atomide.com>,
        Thor Thayer <tthayer@opensource.altera.com>,
        David Lechner <david@lechnology.com>,
        Jan Kiszka <jan.kiszka@siemens.com>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>
Subject: Re: [PATCH] serial: Do not treat the IIR register as a bitfield
Message-ID: <20170330141153.mvxa6iqj72hnhlu3@thunk.org>
Mail-Followup-To: Theodore Ts'o <tytso@mit.edu>,
        Olliver Schinagl <oliver@schinagl.nl>, Vignesh R <vigneshr@ti.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Alexandre Courbot <gnurou@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        "dev@linux-sunxi.org" <dev@linux-sunxi.org>,
        Ed Blake <ed.blake@imgtec.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexander Sverdlin <alexander.sverdlin@nokia.com>,
        Yegor Yefremov <yegorslists@googlemail.com>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@intel.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Heiko Stuebner <heiko@sntech.de>, Jason Uy <jason.uy@broadcom.com>,
        Douglas Anderson <dianders@chromium.org>,
        Peter Hurley <peter@hurleysoftware.com>,
        Tony Lindgren <tony@atomide.com>,
        Thor Thayer <tthayer@opensource.altera.com>,
        David Lechner <david@lechnology.com>,
        Jan Kiszka <jan.kiszka@siemens.com>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>,
        "sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>
References: <20170329184431.6226-1-oliver@schinagl.nl>
 <6be65e8b-eea4-08ed-0b30-5c0608764a83@ti.com>
 <D694FA74-1F31-4B57-8858-2DBE8DE57D45@schinagl.nl>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <D694FA74-1F31-4B57-8858-2DBE8DE57D45@schinagl.nl>
User-Agent: NeoMutt/20170113 (1.7.2)
X-SA-Exim-Connect-IP: <locally generated>
X-SA-Exim-Mail-From: tytso@thunk.org
X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1575
Lines: 46

While you're fixing this, there's a bug in samples/vfio-mdev/mtty.c:

		u8 ier = mdev_state->s[index].uart_reg[UART_IER];
		*buf = 0;

		mutex_lock(&mdev_state->rxtx_lock);
		/* Interrupt priority 1: Parity, overrun, framing or break */
		if ((ier & UART_IER_RLSI) && mdev_state->s[index].overrun)
			*buf |= UART_IIR_RLSI;

		/* Interrupt priority 2: Fifo trigger level reached */
		if ((ier & UART_IER_RDI) &&
		    (mdev_state->s[index].rxtx.count ==
		      mdev_state->s[index].intr_trigger_level))
			*buf |= UART_IIR_RDI;

		/* Interrupt priotiry 3: transmitter holding register empty */
		if ((ier & UART_IER_THRI) &&
		    (mdev_state->s[index].rxtx.head ==
				mdev_state->s[index].rxtx.tail))
			*buf |= UART_IIR_THRI;

		/* Interrupt priotiry 4: Modem status: CTS, DSR, RI or DCD  */
		if ((ier & UART_IER_MSI) &&
		    (mdev_state->s[index].uart_reg[UART_MCR] &
				 (UART_MCR_RTS | UART_MCR_DTR)))
			*buf |= UART_IIR_MSI;

		/* bit0: 0=> interrupt pending, 1=> no interrupt is pending */
		if (*buf == 0)
			*buf = UART_IIR_NO_INT;

It's treating the UART_IIR_* fields as a bitmask which is bad enough,
but in the "Interrupt priority 4" case, UART_IIR_MSI is zero, so 
"*buf |= UART_IIR_MSI" is a no-op.   And in the case where the modem
status interrupt is the only thing set, *buf will be 0, and UART_IIR_NO_INT
gets set erroneously.

So this is another example of the bug of trying to treat the
UART_IIR_* fields as a bitmask....

Yes, it's only sample code, but best fix it now before it gets copied
elsewhere and metastisizes.   :-)

							- Ted