Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752069AbaBBR3o (ORCPT ); Sun, 2 Feb 2014 12:29:44 -0500 Received: from smtp1-g21.free.fr ([212.27.42.1]:59962 "EHLO smtp1-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751862AbaBBR3n convert rfc822-to-8bit (ORCPT ); Sun, 2 Feb 2014 12:29:43 -0500 Date: Sun, 2 Feb 2014 18:30:00 +0100 From: Jean-Francois Moine To: Russell King - ARM Linux Cc: dri-devel@lists.freedesktop.org, Dave Airlie , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Rob Clark Subject: Re: [PATCH v5 02/23] drm/i2c: tda998x: check more I/O errors Message-ID: <20140202183000.1cf9ca9c@armhf> In-Reply-To: <20140202162057.GE26684@n2100.arm.linux.org.uk> References: <9ebf1fdd613b5747aefb3ee21c9c246d102f1a47.1390986082.git.moinejf@free.fr> <20140202162057.GE26684@n2100.arm.linux.org.uk> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2 Feb 2014 16:20:58 +0000 Russell King - ARM Linux wrote: > On Sat, Jan 25, 2014 at 06:14:45PM +0100, Jean-Francois Moine wrote: > > This patch adds more error checking inn I2C I/O functions. > > In case of I/O error, this permits to avoid writing in bad controller > > pages, a bad chipset detection or looping when getting the EDID. > > I've just looked at this again, and spotted something: > > > -static uint8_t > > +static int > > reg_read(struct tda998x_priv *priv, uint16_t reg) > > { > > uint8_t val = 0; > > - reg_read_range(priv, reg, &val, sizeof(val)); > > + int ret; > > + > > + ret = reg_read_range(priv, reg, &val, sizeof(val)); > > + if (ret < 0) > > + return ret; > > So yes, this can return negative numbers. > > > @@ -1158,8 +1184,11 @@ tda998x_encoder_init(struct i2c_client *client, > > tda998x_reset(priv); > > > > /* read version: */ > > - priv->rev = reg_read(priv, REG_VERSION_LSB) | > > - reg_read(priv, REG_VERSION_MSB) << 8; > > + ret = reg_read(priv, REG_VERSION_LSB) | > > + (reg_read(priv, REG_VERSION_MSB) << 8); > > + if (ret < 0) > > + goto fail; > > + priv->rev = ret; > > Two issues here: > > 1. The additional parens are /really/ not required. > 2. What if reg_read(priv, REG_VERSION_MSB) returns a negative number? > > If we're going to the extent of attempting to make the read/write > functions return errors, we should at least handle errors generated > by them properly, otherwise it's pointless making them return errors. > > ret = reg_read(priv, REG_VERSION_LSB); > if (ret < 0) > goto fail; > > priv->rev = ret; > > ret = reg_read(priv, REG_VERSION_MSB); > if (ret < 0) > goto fail; > > priv->rev |= ret << 8; > > If you want it to look slightly nicer: > > int rev_lo, rev_hi; > > rev_lo = reg_read(priv, REG_VERSION_LSB); > rev_hi = reg_read(priv, REG_VERSION_MSB); > if (rev_lo < 0 || rev_hi < 0) { > ret = rev_lo < 0 ? rev_lo : rev_hi; > goto fail; > } > > priv->rev = rev_lo | rev_hi << 8; > > I'm happy to commit such a change after this patch to clean it up, or if > you want to regenerate your patch 2 and post /just/ that incorporating > this change. I think that my code works correctly: when there is an error, the result of reg_read() is minus the error code, and this error code is always lower than 8388607 (0x7fffff). Then, reg_read() << 8 will always be negative. Otherwise, I may redo a patch about the useless parenthesis. -- Ken ar c'hentañ | ** Breizh ha Linux atav! ** Jef | http://moinejf.free.fr/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/