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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B80E9C43219 for ; Sun, 16 Oct 2022 21:03:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229711AbiJPVDq (ORCPT ); Sun, 16 Oct 2022 17:03:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33858 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229572AbiJPVDo (ORCPT ); Sun, 16 Oct 2022 17:03:44 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E02B367B7; Sun, 16 Oct 2022 14:03:43 -0700 (PDT) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 8387AE65; Sun, 16 Oct 2022 23:03:40 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1665954220; bh=/HjB+raKBthocv/QhAd0ZHFd1QaretPzH2sxa49Rnm8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HHQswEjbNdQK+pIeuX/gPUDU6UkSWamMHeVO69fBmy9ka8tdq0WY4Bh1p9070Pt2K zIUAm28hoSgNMriJl7oGHFfLk16rZTUzjm8xELgK+g8GgPzdRKkz94FkiD9URRysI+ y/0GtnFDio77gnEmEy37hAjxZeTnmQNv4OJkWfOQ= Date: Mon, 17 Oct 2022 00:03:17 +0300 From: Laurent Pinchart To: Sakari Ailus Cc: Prabhakar , Krzysztof Kozlowski , Rob Herring , Mauro Carvalho Chehab , Hans Verkuil , Shawn Tu , Jacopo Mondi , linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Biju Das , Lad Prabhakar Subject: Re: [PATCH v2 4/5] media: i2c: ov5645: Return zero for s_stream(0) Message-ID: References: <20221014183459.181567-1-prabhakar.mahadev-lad.rj@bp.renesas.com> <20221014183459.181567-5-prabhakar.mahadev-lad.rj@bp.renesas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi Sakari, On Sun, Oct 16, 2022 at 08:19:40PM +0000, Sakari Ailus wrote: > On Sun, Oct 16, 2022 at 02:23:13AM +0300, Laurent Pinchart wrote: > > On Sat, Oct 15, 2022 at 09:35:12PM +0000, Sakari Ailus wrote: > > > On Sat, Oct 15, 2022 at 09:25:37AM +0300, Laurent Pinchart wrote: > > > > On Fri, Oct 14, 2022 at 07:34:58PM +0100, Prabhakar wrote: > > > > > From: Lad Prabhakar > > > > > > > > > > Always return zero while stopping the stream as the caller will ignore the > > > > > return value. > > > > > > > > > > This patch drops checking the return value of ov5645_write_reg() and > > > > > continues further in the code path while stopping stream. The user anyway > > > > > gets an error message in case ov5645_write_reg() fails. > > > > > > > > Continuing all the way to pm_runtime_put() is fine, but I don't think > > > > the function should return 0. It's not up to the driver to decide if a > > > > failure would be useful to signal to the caller or not. > > > > > > If the function returns an error when disabling streaming, what is the > > > expected power state of the device after this? > > > > That's up to us to decide :-) > > > > > The contract between the caller and the callee is that the state is not > > > changed if there is an error. > > > > For most APIs, but that's not universal. > > > > > This is a special case as very few callers > > > check the return value for streamoff operation and those that do generally > > > just print something. I've never seen a caller trying to prevent streaming > > > off in this case, for instance. > > > > I think the stream off call should proceed and try to power off the > > device even if an error occurs along the way, i.e. it shouldn't return > > upon the first detected error. > > > > > Of course we could document that streaming off always counts as succeeded > > > (e.g. decreasing device's runtime PM usage_count) while it could return an > > > informational error code. But I wonder if anyone would ever benefit from > > > that somehow. :-) > > > > I think it could be useful to propagate errors up to inform the user > > that something wrong happened. That would involve fixing lots of drivers > > along the call chain though, so there's no urgency for the ov5645 to do > > so, but isn't it better to propagate the error code instead of hiding > > the issue ? > > I also don't think hiding the issue would be the best thing to do, but that > wouldn't likely be a big problem either. > > How about printing a warning in the wrapper while returning zero to the > original caller? This would keep the API intact while still leaving a trace > on something failing. Of course the driver is also free to print whatever > messages it likes. While I think error propagation could be more useful in the long run, printing a message in the wrapper is a good idea. I like centralized error handling, it has a tendency to go wrong when left to individual drivers. -- Regards, Laurent Pinchart