From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kPLu9-0008OI-Th for barebox@lists.infradead.org; Mon, 05 Oct 2020 08:31:35 +0000 From: Ahmad Fatoum References: <20200928154247.15619-1-a.fatoum@pengutronix.de> <20200929073220.GU11648@pengutronix.de> <50c46e25-4b69-2868-e264-72b37b82244e@pengutronix.de> <20200930074847.GH11648@pengutronix.de> Message-ID: <2d080897-cff8-57a9-5dba-556933426595@pengutronix.de> Date: Mon, 5 Oct 2020 10:31:32 +0200 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 1/7] driver: introduce less error-prone dev_get_drvdata alternative To: Sascha Hauer Cc: barebox@lists.infradead.org Hello Sascha, On 9/30/20 3:13 PM, Ahmad Fatoum wrote: > Hi, > > On 9/30/20 9:48 AM, Sascha Hauer wrote: >>> If the match data is a valid pointer: >>> -> It doesn't matter, why we have no match data either way. >>> >>> If the match data is a casted integer (e.g. enum): >>> The driver author should either: >>> -> place the default enum value as first one, >>> so no match data => default >> >> You know that, but "The driver Author" probably doesn't. > > Like with all other functions that return an error code, > the author should check those errors: > > enum lm75_type type = (enum lm75_type)device_get_match_data(dev); > if (type == 0) > return -ENODEV; > > I'd expect they will see that 0 shouldn't be part of the enumeration. > >>> -> should add an initial DEVICE_TYPE_UNKNOWN = 0 in the enum >>> and handle it appropriately >>> >>> I like the function signature like that, I don't really see >>> a need to adjust it. >>> >>>> As you realize in your series some drivers cast the returned value into >>>> an integer type and use 0 as a valid possibility. These need an extra >>>> explanation why we can accept that case. I can think of different >>>> possibilies to get that straight: >>>> >>>> - Put a real pointer into matchdata. This is really preferred as it >>>> motivates people to put flags into a (struct type) matchdata which >>>> doesn't lead to excessive if (type == foo || type == bar || type == >>>> baz) we sometimes see in drivers. >>> >>> We have a real pointer there already. The problem is migrating the >>> existing drivers. >> >> Yes, existing drivers would have to be migrated, that is exactly what I >> am proposing. >> >>> >>>> - Return an ERR_PTR from device_get_match_data(). this is less likely >>>> interpreted as a valid int value >>> >>> Doesn't cover all cases. Also for the normal use, it means >>> you need to have to check with IS_ERR_OR_NULL everywhere to >>> be sure you don't dereference a NULL pointer. >> >> Why that? Just don't return NULL when there's no match data, but return >> -ESOMETHING. > > For the lm75 we would have to do: > > enum lm75_type { TYPE_1, TYPE_2 }; > > const void *match = device_get_match_data(dev); > if (IS_ERR(match)) > return PTR_ERR(match); > enum lm75_type type = (enum lm75_type)match; > > The alternative being: > > enum lm75_type { TYPE_UNKNOWN = 0, TYPE_1, TYPE_2 }; > > enum lm75_type type = (enum lm75_type)device_get_match_data(dev); > if (type == TYPE_UNKNOWN) > return -ENODEV; > > I prefer the second one very much. Gentle ping. > >> >> Sascha >> > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox