From mboxrd@z Thu Jan 1 00:00:00 1970 X-GM-THRID: 6470705412124442624 X-Received: by 10.159.234.68 with SMTP id c4mr499538plr.55.1506934899996; Mon, 02 Oct 2017 02:01:39 -0700 (PDT) X-BeenThere: outreachy-kernel@googlegroups.com Received: by 10.98.134.10 with SMTP id x10ls3456033pfd.3.gmail; Mon, 02 Oct 2017 02:01:39 -0700 (PDT) X-Google-Smtp-Source: AOwi7QBf6QvsZuIvr7II+bYsOd8FxFRaWquM6gkFuYjgbwEyQqIFK83a1khvex44boP9uNqnMUpH X-Received: by 10.101.83.141 with SMTP id x13mr717281pgq.37.1506934899091; Mon, 02 Oct 2017 02:01:39 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1506934899; cv=none; d=google.com; s=arc-20160816; b=gelZe7mUnABt2vTNv6eM+iRrmavdDS7XSTpgmM1LOqlxf2BLNQ7jN+qXLjbimBgEvC wKQxKKZGCd0eKoz9cgqLN52dHhuI5v7q/oreaIBiVZFPPknC9Odhkv9gZaZQPHoSv82e ozluppSnLRGL71b6jNbvYB0qrbuEvD37kEwepAu2YKwJoBxpIYtwXN0xIGaIKjWfaEbA uNLoJujd9tgSxmBSmqHRw7YSYZ9cKc7UGxzBwPRcAvt8vLjyvKti7mV/SUuBWrKaFmR+ tH77slUO2rnW29mGOzpkJmDFKIaCAdPGx7paNFDKuFeiDqV+9w2u7I5igL5OPhkH4bLu K06w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:message-id:date:references:organization:in-reply-to :subject:to:from:arc-authentication-results; bh=/aVojGLhfenQpvBrjOdyCe6Vnh9gV4tOQirEjQskXTY=; b=v57gFv3vRsLlLiw2tlQxXbqGPf3oqtrCta277Ubb2BRD6iaGmN9yJs6JBZtUZAwSRY 9/HZIb2dp9X2ScrcuLipbNtXqET4MyJVOC7Wb5ayA0SMYF99tJIqz7W71Xe6s8qxJJZE Uv5ke4VG8wxRMQAdtYimYrsHTTeRWWdaGVst4hCvbY8OuxsdnPGlcQyKzMLR3qLGgaPv zkjOz+f/8O1I/wLjTcoBwyKBrr7WJjSS1ba7nNhnv1EX5MylU8ughrapayalH3a39Udq QC8vek/wWwyFe5QC1QKtjkxrSK2MWnILYMBq1ovuLQO/td/jHmDeO+iHQnghanE37srF IRlA== ARC-Authentication-Results: i=1; gmr-mx.google.com; spf=pass (google.com: domain of jani.nikula@intel.com designates 134.134.136.65 as permitted sender) smtp.mailfrom=jani.nikula@intel.com Return-Path: Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by gmr-mx.google.com with ESMTPS id c200si989467pfb.14.2017.10.02.02.01.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Oct 2017 02:01:39 -0700 (PDT) Received-SPF: pass (google.com: domain of jani.nikula@intel.com designates 134.134.136.65 as permitted sender) client-ip=134.134.136.65; Authentication-Results: gmr-mx.google.com; spf=pass (google.com: domain of jani.nikula@intel.com designates 134.134.136.65 as permitted sender) smtp.mailfrom=jani.nikula@intel.com Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Oct 2017 02:01:25 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,468,1500966000"; d="scan'208";a="905798412" Received: from jnikula-mobl2.fi.intel.com (HELO localhost) ([10.237.72.62]) by FMSMGA003.fm.intel.com with ESMTP; 02 Oct 2017 02:01:22 -0700 From: Jani Nikula To: Daniel Thompson , Meghana Madhyastha , daniel@ffwll.ch, noralf@tronnes.org, outreachy-kernel@googlegroups.com, dri-devel@lists.freedesktop.org, Lee Jones Subject: Re: [PATCH v7 1/3] backlight: Add IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE) In-Reply-To: <527a54b8-d67a-651c-3326-4780b9f3cfc4@linaro.org> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <7a6311819f8eea0b2845c25cca72324b25e63e13.1506878301.git.meghana.madhyastha@gmail.com> <527a54b8-d67a-651c-3326-4780b9f3cfc4@linaro.org> Date: Mon, 02 Oct 2017 12:00:54 +0300 Message-ID: <87o9pp6i0p.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain On Mon, 02 Oct 2017, Daniel Thompson wrote: > So I'm coming to this patchset cold but can you explain *why* something > wants to call of_find_backlight_by_node() when there is no backlight > support enabled. Why isn't the code that called is conditional on > BACKLIGHT_CLASS_DEVICE? > > The undefined symbol issue is a pain but to be honest I'd rather solve > the use of undefined symbols by avoiding declaring them; this making > them into compile errors rather than link errors. Typically the kernel header files define static inline stubs of the functions when the actual functions aren't configured/built. The code using the functions looks the same regardless of the config option, and handles the -ENODEV or NULL or whatever returns from the stubs gracefully. With the inlines, the compiler can usually throw out much of the code anyway. In this regard, the backlight interface is an exception, forcing the callers to wrap the code around IS_ENABLED(BACKLIGHT_CLASS_DEVICE), not the rule. BR, Jani. -- Jani Nikula, Intel Open Source Technology Center From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jani Nikula Subject: Re: [PATCH v7 1/3] backlight: Add IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE) Date: Mon, 02 Oct 2017 12:00:54 +0300 Message-ID: <87o9pp6i0p.fsf@intel.com> References: <7a6311819f8eea0b2845c25cca72324b25e63e13.1506878301.git.meghana.madhyastha@gmail.com> <527a54b8-d67a-651c-3326-4780b9f3cfc4@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by gabe.freedesktop.org (Postfix) with ESMTPS id E39F66E2D9 for ; Mon, 2 Oct 2017 09:01:25 +0000 (UTC) In-Reply-To: <527a54b8-d67a-651c-3326-4780b9f3cfc4@linaro.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Daniel Thompson , Meghana Madhyastha , daniel@ffwll.ch, noralf@tronnes.org, outreachy-kernel@googlegroups.com, dri-devel@lists.freedesktop.org, Lee Jones List-Id: dri-devel@lists.freedesktop.org T24gTW9uLCAwMiBPY3QgMjAxNywgRGFuaWVsIFRob21wc29uIDxkYW5pZWwudGhvbXBzb25AbGlu YXJvLm9yZz4gd3JvdGU6Cj4gU28gSSdtIGNvbWluZyB0byB0aGlzIHBhdGNoc2V0IGNvbGQgYnV0 IGNhbiB5b3UgZXhwbGFpbiAqd2h5KiBzb21ldGhpbmcgCj4gd2FudHMgdG8gY2FsbCBvZl9maW5k X2JhY2tsaWdodF9ieV9ub2RlKCkgd2hlbiB0aGVyZSBpcyBubyBiYWNrbGlnaHQgCj4gc3VwcG9y dCBlbmFibGVkLiBXaHkgaXNuJ3QgdGhlIGNvZGUgdGhhdCBjYWxsZWQgaXMgY29uZGl0aW9uYWwg b24gCj4gQkFDS0xJR0hUX0NMQVNTX0RFVklDRT8KPgo+IFRoZSB1bmRlZmluZWQgc3ltYm9sIGlz c3VlIGlzIGEgcGFpbiBidXQgdG8gYmUgaG9uZXN0IEknZCByYXRoZXIgc29sdmUgCj4gdGhlIHVz ZSBvZiB1bmRlZmluZWQgc3ltYm9scyBieSBhdm9pZGluZyBkZWNsYXJpbmcgdGhlbTsgdGhpcyBt YWtpbmcgCj4gdGhlbSBpbnRvIGNvbXBpbGUgZXJyb3JzIHJhdGhlciB0aGFuIGxpbmsgZXJyb3Jz LgoKVHlwaWNhbGx5IHRoZSBrZXJuZWwgaGVhZGVyIGZpbGVzIGRlZmluZSBzdGF0aWMgaW5saW5l IHN0dWJzIG9mIHRoZQpmdW5jdGlvbnMgd2hlbiB0aGUgYWN0dWFsIGZ1bmN0aW9ucyBhcmVuJ3Qg Y29uZmlndXJlZC9idWlsdC4gVGhlIGNvZGUKdXNpbmcgdGhlIGZ1bmN0aW9ucyBsb29rcyB0aGUg c2FtZSByZWdhcmRsZXNzIG9mIHRoZSBjb25maWcgb3B0aW9uLCBhbmQKaGFuZGxlcyB0aGUgLUVO T0RFViBvciBOVUxMIG9yIHdoYXRldmVyIHJldHVybnMgZnJvbSB0aGUgc3R1YnMKZ3JhY2VmdWxs eS4gV2l0aCB0aGUgaW5saW5lcywgdGhlIGNvbXBpbGVyIGNhbiB1c3VhbGx5IHRocm93IG91dCBt dWNoIG9mCnRoZSBjb2RlIGFueXdheS4KCkluIHRoaXMgcmVnYXJkLCB0aGUgYmFja2xpZ2h0IGlu dGVyZmFjZSBpcyBhbiBleGNlcHRpb24sIGZvcmNpbmcgdGhlCmNhbGxlcnMgdG8gd3JhcCB0aGUg Y29kZSBhcm91bmQgSVNfRU5BQkxFRChCQUNLTElHSFRfQ0xBU1NfREVWSUNFKSwgbm90CnRoZSBy dWxlLgoKQlIsCkphbmkuCgoKLS0gCkphbmkgTmlrdWxhLCBJbnRlbCBPcGVuIFNvdXJjZSBUZWNo bm9sb2d5IENlbnRlcgpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fXwpkcmktZGV2ZWwgbWFpbGluZyBsaXN0CmRyaS1kZXZlbEBsaXN0cy5mcmVlZGVza3RvcC5v cmcKaHR0cHM6Ly9saXN0cy5mcmVlZGVza3RvcC5vcmcvbWFpbG1hbi9saXN0aW5mby9kcmktZGV2 ZWwK