From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@kernel.org>
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 7B30BC433F5
	for <linux-kernel@archiver.kernel.org>; Mon, 18 Apr 2022 22:10:16 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S230446AbiDRWMw (ORCPT <rfc822;linux-kernel@archiver.kernel.org>);
        Mon, 18 Apr 2022 18:12:52 -0400
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60400 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S230386AbiDRWMc (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 18 Apr 2022 18:12:32 -0400
Received: from foss.arm.com (foss.arm.com [217.140.110.172])
        by lindbergh.monkeyblade.net (Postfix) with ESMTP id 71CB320F43
        for <linux-kernel@vger.kernel.org>; Mon, 18 Apr 2022 15:09:43 -0700 (PDT)
Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14])
        by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CD81D1042;
        Mon, 18 Apr 2022 15:09:42 -0700 (PDT)
Received: from [10.57.41.251] (unknown [10.57.41.251])
        by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A92383F766;
        Mon, 18 Apr 2022 15:09:39 -0700 (PDT)
Message-ID: <1d9a2146-9e48-ba97-d049-5d2332ebbd3a@arm.com>
Date:   Mon, 18 Apr 2022 23:09:36 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101
 Thunderbird/91.8.0
Subject: Re: [PATCH 02/13] iommu: Move bus setup to IOMMU device registration
Content-Language: en-GB
To:     Lu Baolu <baolu.lu@linux.intel.com>, joro@8bytes.org,
        will@kernel.org
Cc:     iommu@lists.linux-foundation.org, sven@svenpeter.dev,
        robdclark@gmail.com, m.szyprowski@samsung.com,
        yong.wu@mediatek.com, mjrosato@linux.ibm.com,
        gerald.schaefer@linux.ibm.com, zhang.lyra@gmail.com,
        thierry.reding@gmail.com, vdumpa@nvidia.com,
        jean-philippe@linaro.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
References: <cover.1649935679.git.robin.murphy@arm.com>
 <e607a32be8e84c56d65160902f4bd3fb434ee9d3.1649935679.git.robin.murphy@arm.com>
 <d838c7f8-2d31-2327-9b4d-c05b06a516bb@linux.intel.com>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <d838c7f8-2d31-2327-9b4d-c05b06a516bb@linux.intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 2022-04-16 01:04, Lu Baolu wrote:
> On 2022/4/14 20:42, Robin Murphy wrote:
>> @@ -1883,27 +1900,12 @@ static int iommu_bus_init(struct bus_type *bus)
>>    */
>>   int bus_set_iommu(struct bus_type *bus, const struct iommu_ops *ops)
>>   {
>> -    int err;
>> -
>> -    if (ops == NULL) {
>> -        bus->iommu_ops = NULL;
>> -        return 0;
>> -    }
>> -
>> -    if (bus->iommu_ops != NULL)
>> +    if (bus->iommu_ops && ops && bus->iommu_ops != ops)
>>           return -EBUSY;
>>       bus->iommu_ops = ops;
> 
> Do we still need to keep above lines in bus_set_iommu()?

It preserves the existing behaviour until each callsite and its 
associated error handling are removed later on, which seems like as good 
a thing to do as any. Since I'm already relaxing iommu_device_register() 
to a warn-but-continue behaviour while it keeps the bus ops on 
life-support internally, I figured not changing too much at once would 
make it easier to bisect any potential issues arising from this first step.

Thanks,
Robin.