From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Cameron Subject: Re: [PATCH] TSL2550 driver bugfix Date: Tue, 30 Jun 2009 16:41:26 +0000 Message-ID: <4A4A4036.3000408@cam.ac.uk> References: <4A4A2FBC.1060804@valueteam.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4A4A2FBC.1060804-EZxuzQJkuwwybS5Ee8rs3A@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Michele De Candia (VT)" Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, giometti-k2GhghHVRtY@public.gmane.org List-Id: linux-i2c@vger.kernel.org Michele De Candia (VT) wrote: > Hi all, > > I've tested TSL2550 driver and I've found a bug: when light is off, > returned value from tsl2550_calculate_lux function is -1 when it should > be 0 (sensor correctly read that light was off). > > I think the bug is that a zero c0 value (approximated value of ch0) is > misinterpreted as an error. > I'm attaching you a patch that fixes the bug. > > Regards, > Michele Jr De Candia Sounds reasonable, but I think a stray line got away in your patch (see below) Not to mention, if the c1 <= c0 check is still valid, should you not also confirm that c1 == 0 as well? Perhaps reverse the ordering? if (c1 <= c0) if(c0) { r = c1* 128 / c0; lux = ((c0 - c1) * ratio_lut[r]) / 256; } else lux = 0; else return -1; Signed-off-by: Michele Jr De Candia diff --git a/drivers/i2c/chips/tsl2550.c b/drivers/i2c/chips/tsl2550.c index 1a9cc13..6bad072 100644 --- a/drivers/i2c/chips/tsl2550.c +++ b/drivers/i2c/chips/tsl2550.c @@ -189,10 +189,16 @@ static int tsl2550_calculate_lux(u8 ch0, u8 ch1) u8 r = 128; /* Avoid division by 0 and count 1 cannot be greater than count 0 */ - if (c0 && (c1 <= c0)) - r = c1 * 128 / c0; - else - return -1; + if (c0) { + if (c1 <= c0) + r = c1 * 128 / c0; + else + return -1; + + /* Calculate LUX */ + lux = ((c0 - c1) * ratio_lut[r]) / 256; + } + else lux = 0; This last line should have been removed I think? /* Calculate LUX */ lux = ((c0 - c1) * ratio_lut[r]) / 256; --- Jonathan Cameron