Message-ID: <ced8713f-69de-e48a-37eb-4f844e651b6b@suse.com>
Date:   Thu, 16 Mar 2023 15:01:25 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH v2 1/1] Guard pci_create_sysfs_dev_files with atomic value
Content-Language: en-US
To:     Alexander Stein <alexander.stein@ew.tq-group.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Oliver Neukum <oneukum@suse.com>
Cc:     Korneliusz Osmenda <korneliuszo@gmail.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230316091540.494366-1-alexander.stein@ew.tq-group.com>
 <4888964.44csPzL39Z@steina-w> <90e97b96-2918-294a-0e71-33a42f28d8a8@suse.com>
 <3607385.usQuhbGJ8B@steina-w>
From:   Oliver Neukum <oneukum@suse.com>
In-Reply-To: <3607385.usQuhbGJ8B@steina-w>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?MVk0MXhSVEkrZkI4TVJUMTFBWEJGT3hyYjlOaDVpUnRVcVE3T093bXoyNFYy?=
 =?utf-8?B?cGw5ZHN2UmxaZmJ1dGlLTnNzT2ZtODdKWTVLOWFEdHdvTDQ4ZEQ5eHo1amJl?=
 =?utf-8?B?WnlMVFZQTllkSjNhcGptL2JZVFBVUzQvM2E0SFpIVEc2ZnBpeG9EekxYbUs0?=
 =?utf-8?B?NGFPWWlEdmluaFZ6QUZXTHJibDBobk1STHZXNTdmNXhSY3g1V1VaZUUrRzNS?=
 =?utf-8?B?cWYrOXg2R1VyUDRjNEp5bmp6TmpvWmtLd0QrcUIyWG4wL2l0NzV4UjJZa295?=
 =?utf-8?B?cE5qemtNb2JBeDQ5OFpFcU8zOTNINjNQYlRrVnowazY5YnZSQ1dudU5nT3Bi?=
 =?utf-8?B?Tmo3TXJJNURnaWxLWDJOTjNGVmFISTZjc01ueFBzL3AwcTNKTVMzTXVha0hW?=
 =?utf-8?B?YlhsTVB4d1RFdnhBVFlSNHYvZ3ZNUWs3WFJYYkRYRSt1OWVrdm83MXBSWm00?=
 =?utf-8?B?c2ZtbXFKYkxzQnhlMGFTTVp6VmVrQmlialZoWUtzWGlxWjV5a3dxRTVwcWlL?=
 =?utf-8?B?U1E3T3JFYU90UmtwZE51ODZSRUdKbHVrMVN0SUs5LzVNTGdSWXVTYVV0RUI3?=
 =?utf-8?B?eUVHbSt3NVZsc2JHUHBYb2N3TEU2c2tyOUNXa1JwbWJMRnRDSnZuZVNudlRx?=
 =?utf-8?B?Y0NZczhTQkFZUk12NTVtZDNFRzg0a3Y4MVZldDE1cHBldW40NjV0a0lvWjhT?=
 =?utf-8?B?R1ZsUU9MSUJ5dnlucG9SVWNkdlZOcnJrY0Y0NGFxSDVkaDBvQk85ekQ3WTVI?=
 =?utf-8?B?R0hmM2RIeEdkMDZMZzBxbURmclZONmdYTm5GVzB5RFhyNzZkVkNiS0pPQ3Fy?=
 =?utf-8?B?ckR4RldpVkRJcUpaempISXFFWnRjY2JFQVFHbjFHS0lBYlFTYVB2MHVCUTQr?=
 =?utf-8?B?clVWdUZwWGdaR3Q1dHZxbnpWcmwxT01nMVZaMkZSdnZQUndpTitEbkRTS1Zq?=
 =?utf-8?B?a2lYdnc4U0szRmQ0cVdFVXFXQXJ3THlOdlJhY3BldHhmNGZ4TDQ3dkVYbUpL?=
 =?utf-8?B?Z1RPdkpRWkQ3Zmw1L0owNU9ma3M1Tm8zcXludGJHWmVRZ0NsTjZnZkVVSUIw?=
 =?utf-8?B?MFRWa1ptR3Faemw2ekdnSWlVUFhxU3pnNXUwL3JGNENhZ29rMnZOblVkcG1z?=
 =?utf-8?B?Zk9sZjAxYzRERnJyMXF5N29kNUlxNXBHNmQwcFJnM3dtUENHVGlUZndrZXdk?=
 =?utf-8?B?R2FLQmNtMzliOURsUlk3ZmU1Q3dmVkYrSUszMDdxWlFoWW02YmRMVWkxSUM1?=
 =?utf-8?B?V2VXY3E3R283NEp4dkN0WWk1dVF3WnhVWkgybmdDSHRxUmErTmRkc2MzTzFZ?=
 =?utf-8?B?Tk9VV2RrZVQ2RTN6b3ZxdE1zM2tSc3Q1T3l2OEFGbTBiZjJRSjlFMElRbmFn?=
 =?utf-8?B?V1RjVjQ0TTlydmdpUStXenl2WFc4MDd6UDhrWVdWbjEyRFhta0lqSiswcTZt?=
 =?utf-8?B?SG4yU1ArZWFXaVhtREZmL1BDOXk5Q25oREpwNURjdXczNTFKUmlXc3BJdlpG?=
 =?utf-8?B?L3ZSakw2VDBXcVprWThmRzNKMDdGSU1IODBzMEFwTEMzVG5LbDROMFY2YVgw?=
 =?utf-8?B?TGtvOGZQMnVMN0gzckRrUS8rSGYvUFR0RWxqOFZXdXNUWnU0Nnl3TDN3ZWtp?=
 =?utf-8?B?dDB4ZTBqU3M2ekx2aEx5enJncE5rSjVnaUpZb0VLTFpWa3FZcTVtUTF2YzIy?=
 =?utf-8?B?ajBpQzdyNmlzeDdlSldSejNPdG8zL01xR1Q5bks5cElXcWxST0NSUGl6Kys1?=
 =?utf-8?B?UE5TL1pKMDhWL080bE13L0l3c3VkdDQxTzVPODhMbFpFaGliN1pVTjFWM2Yy?=
 =?utf-8?B?VFpvRDF1V24xNkRkekJ0K2QwL01ISGZwQ3JXOFVWS1J6T2d4NGdwYlFPditY?=
 =?utf-8?B?cGV5djRKcWVrZEJlNEhyWStEdDZvMGlqQ09adjRiLy82WS9vWWtNbitWVHYx?=
 =?utf-8?B?cWQ0aVEvbnc1UlZybUVaclg5NEJqeVlrejZZWmErSitydWpUUzlWSUUybXUw?=
 =?utf-8?B?dEttSzVXUEJ4U2dhQ0J6eEZqVzdpcEc4ZWFtYVFKZkduRmptdTZ0T29kUDVU?=
 =?utf-8?B?bHZ2QytFZExodFFwTE5YZC9rWWFDZERnNGQ1RWw1NUJENWlrVEhpaVFMV05R?=
 =?utf-8?B?NXY4R2FBM0JSRHRVNGFKbHpqeTBtanQ1RklCTlBqcUhuSzBDN0QxdXBPc2t6?=
 =?utf-8?Q?txQn2Dw6M+dhDGFGh7/OOF7Obp48u6ZkisycOBnhy1u1?=
X-OriginatorOrg: suse.com
X-MS-Exchange-CrossTenant-Network-Message-Id: f0833c23-0d79-4039-1708-08db2626ef8d
X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB7104.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Mar 2023 14:01:27.4545
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 1AmgWoAeEDkgm7cXXJie/t83AZuHrv1kXZ5R23Bbsc49PgogjnaXe/FbV0HFxeCaOuVcgI8jstdZpJziHMbkwg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1PR04MB7213
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 16.03.23 14:16, Alexander Stein wrote:

> But isn't the root bridge discovered by the driver (pci-imx6 in this case) for
> that? And the driver probe path eventually calls into the sysfs file creation.
> I compared the file creation to usb, as this is a discoverable bus as well.
> There is no special initialization regarding sysfs.

If you discover a bus system you always have the option of creating of virtual
hotplug event for the root hub or host controller.
But for PCI that is a bad design choice. USB is different.

> If, for some reason, the device enumeration for PCI bus during imx6_pcie_probe
> is delayed after pci_sysfs_init initcall, this initcall essentially does
> nothing, no devices or busses to iterate. Which means the complete pcie sysfs

On your specific system. You cannot use that as a model for all systems.

> creation is done from bridge probe path. There is no reason to iterate over
> discovered PCIe devices/busses separately.

If there is no other PCI device, the loop is a nop. But otherwise it is necessary.

>>> So technically the device is not probed from within a initcall but a
>>> kthread. It is set to be probed asynchronous in imx6_pcie_driver.
>>
>> That may be the problem, respectively that system is incomplete
>> You are registering a PCI bridge. The PCI subsystem should be
>> done setting up when you run. That is just a simple dependency.
> 
> Is there such an dependency in the first place? I can't see anything, even the
> late_initcall to pci_resource_alignment_sysfs_init is a different matter.

On your hardware, yes. In the kernel, no.
That is the very point. The kernel is missing a way to represent a dependency.

	Regards
		Oliver