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 X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0FE25C43603 for ; Tue, 17 Dec 2019 08:56:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D38F92072D for ; Tue, 17 Dec 2019 08:56:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="bPoj1k7J" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727130AbfLQI4c (ORCPT ); Tue, 17 Dec 2019 03:56:32 -0500 Received: from mail26.static.mailgun.info ([104.130.122.26]:23525 "EHLO mail26.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727070AbfLQI4b (ORCPT ); Tue, 17 Dec 2019 03:56:31 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1576572990; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=ZJq7Qp3bn1KsgMY+MZCRUXUmBAGCDF5Rh8QzjkblaaY=; b=bPoj1k7Je11sJPa9xjm5pwnhuZmpKhA2yLSgx/L4AMvuguhtTbVan2EiUZDzZDFASJLqD1Is Vonxa8BFtaZcY6ly2gJ+foXq6VW27SoYPgcH+5x8LZmrg/2TiVbpJYQzqN/FGuBn0pu112I+ n87MFONvYhGGMRhzm8rj2UhiuMM= X-Mailgun-Sending-Ip: 104.130.122.26 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5df8983b.7f2a43eacbc8-smtp-out-n02; Tue, 17 Dec 2019 08:56:27 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 703BFC447AE; Tue, 17 Dec 2019 08:56:25 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: cang) by smtp.codeaurora.org (Postfix) with ESMTPSA id 6B16BC433CB; Tue, 17 Dec 2019 08:56:23 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Tue, 17 Dec 2019 16:56:23 +0800 From: cang@codeaurora.org To: Bart Van Assche Cc: Bjorn Andersson , asutoshd@codeaurora.org, nguyenb@codeaurora.org, rnayak@codeaurora.org, linux-scsi@vger.kernel.org, kernel-team@android.com, saravanak@google.com, salyzyn@google.com, Alim Akhtar , Avri Altman , Pedro Sousa , "James E.J. Bottomley" , "Martin K. Petersen" , Evan Green , Kishon Vijay Abraham I , Stephen Boyd , Stanley Chu , Vignesh Raghavendra , Bean Huo , Venkat Gopalakrishnan , Tomas Winkler , Arnd Bergmann , open list Subject: Re: [PATCH v2 2/3] scsi: ufs: Modulize ufs-bsg In-Reply-To: <62933901-fcdf-b5ae-431d-e1fbfc897128@acm.org> References: <1576054123-16417-1-git-send-email-cang@codeaurora.org> <0101016ef425ef65-5c4508cc-5e76-4107-bb27-270f66acaa9a-000000@us-west-2.amazonses.com> <20191212045357.GA415177@yoga> <0101016ef8b2e2f8-72260b08-e6ad-42fc-bd4b-4a0a72c5c9b3-000000@us-west-2.amazonses.com> <20191212063703.GC415177@yoga> <5691bfa1-42e5-3c5f-2497-590bcc0cb2b1@acm.org> <926dd55d8d0dc762b1f6461495fc747a@codeaurora.org> <62933901-fcdf-b5ae-431d-e1fbfc897128@acm.org> Message-ID: X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-12-17 01:22, Bart Van Assche wrote: > On 12/15/19 8:36 PM, cang@codeaurora.org wrote: >> On 2019-12-16 05:49, Bart Van Assche wrote: >>> On 2019-12-11 22:37, Bjorn Andersson wrote: >>>> It's the asymmetry that I don't like. >>>> >>>> Perhaps if you instead make ufshcd platform_device_register_data() >>>> the >>>> bsg device you would solve the probe ordering, the remove will be >>>> symmetric and module autoloading will work as well (although then >>>> you >>>> need a MODULE_ALIAS of platform:device-name). >>> >>> Hi Bjorn, >>> >>> From Documentation/driver-api/driver-model/platform.rst: >>> "Platform devices are devices that typically appear as autonomous >>> entities in the system. This includes legacy port-based devices and >>> host bridges to peripheral buses, and most controllers integrated >>> into system-on-chip platforms.  What they usually have in common >>> is direct addressing from a CPU bus.  Rarely, a platform_device will >>> be connected through a segment of some other kind of bus; but its >>> registers will still be directly addressable." >>> >>> Do you agree that the above description is not a good match for the >>> ufs-bsg kernel module? >> >> I missed this one. >> How about making it a plain device and add it from ufs driver? > > Hi Can, > > Since the ufs_bsg kernel module already creates one device node under > /dev/bsg for each UFS host I don't think that we need to create any > additional device nodes for ufs-bsg devices. My proposal is to modify > the original patch 2/3 from this series as follows: > * Use module_init() instead of late_initcall_sync(). > * Remove the ufshcd_get_hba_list_lock() and > ufshcd_put_hba_list_unlock() functions. > * Implement a notification mechanism in the UFS core that invokes a > callback function after an UFS host has been created and also after > an > UFS host has been removed. > * Register for these notifications from inside the ufs-bsg driver. > * During registration for notifications, invoke the UFS host creation > callback function for all known UFS hosts. > * If the UFS core is unloaded, invoke the UFS host removal callback > function for all known UFS hosts. > > I think there are several examples of similar notification mechanisms > in the Linux kernel, e.g. the probe and remove callback functions in > struct pci_driver. > > Bart. Hi Bart, Even in the current ufs_bsg.c, it creates two devices, one is ufs-bsg, one is the char dev node under /dev/bsg. Why this becomes a problem after make it a module? I took a look into the pci_driver, it is no different than making ufs-bsg a plain device. The only special place about pci_driver is that it has its own probe() and remove(), and the probe() in its bus_type calls the probe() in pci_driver. Meaning the bus->probe() is an intermediate call used to pass whatever needed by pci_driver->probe(). Of course we can also do this, but isn't it too much for ufs-bsg? For our case, calling set_dev_drvdata(bsg_dev, hba) to pass hba to ufs_bsg.c would be enough. If you take a look at the V3 patch, the change makes the ufs_bsg.c much conciser. platform_device_register_data() does everything for us, initialize the device, set device name, provide the match func, bus type and release func. Since ufs-bsg is somewhat not a platform device, we can still add it as a plain device, just need a few more lines to get it initialized. This allows us leverage kernel's device driver model. Just like Greg commented, we don't need to re-implement the mechanism again. Thanks, Can Guo.