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 0524CC4332F for ; Mon, 17 Oct 2022 07:41:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230122AbiJQHlX (ORCPT ); Mon, 17 Oct 2022 03:41:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60968 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230022AbiJQHlU (ORCPT ); Mon, 17 Oct 2022 03:41:20 -0400 Received: from mail-ej1-x634.google.com (mail-ej1-x634.google.com [IPv6:2a00:1450:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BBB2813DDF; Mon, 17 Oct 2022 00:41:17 -0700 (PDT) Received: by mail-ej1-x634.google.com with SMTP id bj12so22850104ejb.13; Mon, 17 Oct 2022 00:41:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=jp8HrSCso1cEfmmqdQBEdUtj0Bbq01HpoZXdky0tskI=; b=fbtJmyV8qM0M7KbwD36UBnvc5tzo0doZXFZ/rKdCDx8J3dYTtTSn/IYu+gZtMCBLgp lQvG5PJDQN7Yrzkbc8NJ0q6iGhSvRMMKQnlQjzKIbd5V+AF6ny6Pwsvs2V4+pWCEFIC+ gaqbTTfnIQClaSTJVTF71H9Mfc9yqtRPvqIm4F7sHF1JaXtTiuW99vHpazTA9lqm9za8 ac8ZWPMB+cf0oq+dp0GoqNYrZj5ldg8eZLQ2JVAoG+z9Bk47MrXDNLLf3OX+ung1X3aK an7QqerLK5UB69vodObQcJB8xyhiv2AjbIjDY2RkhFo7jLrkwK4gz5XJ1u36pFoNZY2z AQjA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=jp8HrSCso1cEfmmqdQBEdUtj0Bbq01HpoZXdky0tskI=; b=m0QRq3sghvRHaNL0NC7WBMqf+0UxmOpaqStSWPA5icmxipCRqPzFwr2auLnPAa6iUx v6bY8RXPgTie1BuHEMim+1UusAVDoS78M83d13pAdeQ6WYlHWGizwa1+vF3F4Wdj9yub uuoedS1y36rGIX82vKaE0nwFADTBhKVtGlsWgDU6LZWXBFCGrqpFk8GdZazP+PQTrPUk YRyBV1wO9M74nzhJUYaKo+Hi81QssttjzBb6qN44YHW20COmOKXdOWDjU0x5Mj2OnbQX w4Ooak/cK1kEIF3navrqDSPuoccIg4kAPLKLbZD5kdEdw97rhw5PZ+YyIp9sqg9XIu5R jMqA== X-Gm-Message-State: ACrzQf36H+LSUAmIsVCxKH0afZkR+5hlecvEzfv2A1bSd51dxhz7F373 7HLG0tD3/fckhI/7acacLwIW8r6FoFT/zYo+iUY= X-Google-Smtp-Source: AMsMyM71lZzbP/LAJp4Ui5wekihf0780L8XnOegyGGstUHtaFcNanS3NyUllyd/7igndW+Z+Um8u8n5p2XT0oK/PrJA= X-Received: by 2002:a17:906:5a4b:b0:78d:4e5a:d101 with SMTP id my11-20020a1709065a4b00b0078d4e5ad101mr7459289ejc.196.1665992475700; Mon, 17 Oct 2022 00:41:15 -0700 (PDT) MIME-Version: 1.0 References: <20221014183459.181567-1-prabhakar.mahadev-lad.rj@bp.renesas.com> <20221014183459.181567-5-prabhakar.mahadev-lad.rj@bp.renesas.com> In-Reply-To: From: "Lad, Prabhakar" Date: Mon, 17 Oct 2022 08:40:49 +0100 Message-ID: Subject: Re: [PATCH v2 4/5] media: i2c: ov5645: Return zero for s_stream(0) To: Sakari Ailus Cc: Laurent Pinchart , 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sakari, On Mon, Oct 17, 2022 at 8:12 AM Sakari Ailus wrote: > > On Mon, Oct 17, 2022 at 12:03:17AM +0300, Laurent Pinchart wrote: > > 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. > > I can send a patch... > To conclude, for v3 I'll continue down the code path upon error and then report back the error? Cheers, Prabhakar