From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta1.migadu.com (out-171.mta1.migadu.com [95.215.58.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 892B636AF2 for ; Thu, 16 May 2024 10:40:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715856056; cv=none; b=X0AaPt5UjKe/MM+NhXttxG8eqybYK664dKytakjlQKQtBLjuY/b4EVwGDH3Pg5uu1vYn9VBP1KuWm6x9UEpA43n+sPza/DgHKgQBhzHH9TlXvm/qOUDSfp2JHXZNh0dSAUkZMaZ6DOiBdlNqxjQA0rPhsFdTu9LM/SBHrirKKuo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715856056; c=relaxed/simple; bh=sGttAr4KFordtBrDF5gVghngOZmdSmOjdkfoI1eBtII=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lFOqWj4e83WjWc0RzRcdI5+SMCb/Ae9yGvM1ysYEnoq94LhyVuJYILcS2XuuY9guEl4qP1XUwZrySTs0bGPSLkh4kJWKZ6DNZRJnuiZlYR4MO1O7/89UQsP1VA7kN/bW8KWjA4eengvFZC0vmn6eQZ03FMYeR8xKLG0Q4VmMypI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=jrlp5AB4; arc=none smtp.client-ip=95.215.58.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="jrlp5AB4" X-Envelope-To: mripard@kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1715856052; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rNeJ2ZdpLPa8Jx4oYrQIUXFJQZti3fsu6ianHYlk4uM=; b=jrlp5AB46TnutoFegGgEWhaZUDIOwL5m6VvgVbPFGM8/CZgEbT/wfliSMBypIWUrswPDMV 1Ha4bKruEl2QcA1LPH5FQMvQSfNUaeO5hhzoXYnZmMfEExGOyZ0aFrFLQFyE+0/p6cMUTo l1SHmiIXilN3PZ1lP8MRee1YcBKdPog= X-Envelope-To: neil.armstrong@linaro.org X-Envelope-To: dmitry.baryshkov@linaro.org X-Envelope-To: dri-devel@lists.freedesktop.org X-Envelope-To: linux-kernel@vger.kernel.org Message-ID: Date: Thu, 16 May 2024 18:40:45 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 0/2] drm/bridge: Add 'struct device *' field to the drm_bridge structure To: Maxime Ripard Cc: Neil Armstrong , Dmitry Baryshkov , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20240514154045.309925-1-sui.jingfeng@linux.dev> <20240514-scarlet-corgi-of-efficiency-faf2bb@penduick> <20240515-fair-satisfied-myna-480dea@penduick> <20240515-copper-chimpanzee-of-fortitude-ff3dab@penduick> <2c15c859-6b2b-4979-8317-698bf6cc430c@linux.dev> <20240516-intrepid-uptight-tench-0df95e@penduick> Content-Language: en-US, en-AU X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Sui Jingfeng In-Reply-To: <20240516-intrepid-uptight-tench-0df95e@penduick> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hi, On 5/16/24 16:25, Maxime Ripard wrote: > On Wed, May 15, 2024 at 11:19:58PM +0800, Sui Jingfeng wrote: >> Hi, >> >> >> On 5/15/24 22:58, Maxime Ripard wrote: >>> On Wed, May 15, 2024 at 10:53:00PM +0800, Sui Jingfeng wrote: >>>> On 5/15/24 22:30, Maxime Ripard wrote: >>>>> On Wed, May 15, 2024 at 12:53:33AM +0800, Sui Jingfeng wrote: >>>>>> On 2024/5/15 00:22, Maxime Ripard wrote: >>>>>>> Hi, >>>>>>> >>>>>>> On Tue, May 14, 2024 at 11:40:43PM +0800, Sui Jingfeng wrote: >>>>>>>> Because a lot of implementations has already added it into their drived >>>>>>>> class, promote it into drm_bridge core may benifits a lot. drm bridge is >>>>>>>> a driver, it should know the underlying hardware entity. >>>>>>> Is there some actual benefits, or is it theoretical at this point? >>>>>> >>>>>> >>>>>> I think, DRM bridge drivers could remove the 'struct device *dev' >>>>>> member from their derived structure. Rely on the drm bridge core >>>>>> when they need the 'struct device *' pointer. >>>>> >>>>> Sure, but why do we need to do so? >>>>> >>>>> The other thread you had with Jani points out that it turns out that >>>>> things are more complicated than "every bridge driver has a struct >>>>> device anyway", it creates inconsistency in the API (bridges would have >>>>> a struct device, but not other entities), and it looks like there's no >>>>> use for it anyway. >>>>> >>>>> None of these things are deal-breaker by themselves, but if there's only >>>>> downsides and no upside, it's not clear to me why we should do it at all. >>>> >>>> It can reduce boilerplate. >>> >>> You're still using a conditional here. >> >> It's for safety reason, prevent NULL pointer dereference. >> drm bridge can be seen as either a software entity or a device driver. >> >> It's fine to pass NULL if specific KMS drivers intend to see >> drm bridge as a pure software entity, and for internal use only. >> Both use cases are valid. > > Sorry, I don't follow you. We can't NULL dereference a pointer that > doesn't exist. > > Please state why we should merge this series: what does it fix or > improve, aside from the potential gain of making bridges declare one > less pointer in their private structure. We could reduce more. Bridge driver instances also don't have to embed 'struct i2c_client *'. We could use 'to_i2c_client(bridge->dev)' to retrieve the pointer, where needed. > Maxime -- Best regards Sui