linux-kernel - Re: [PATCH v2 2/3] scsi: ufs: Modulize ufs-bsg

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Message-ID: <62933901-fcdf-b5ae-431d-e1fbfc897128@acm.org>
Date:   Mon, 16 Dec 2019 09:22:21 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     cang@...eaurora.org
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Evan Green <evgreen@...omium.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Stephen Boyd <swboyd@...omium.org>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Bean Huo <beanhuo@...ron.com>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] scsi: ufs: Modulize ufs-bsg

On 12/15/19 8:36 PM, cang@...eaurora.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.