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

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Date:   Wed, 18 Dec 2019 02:47:33 +0800
From:   cang@...eaurora.org
To:     Bart Van Assche <bvanassche@....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 2019-12-18 02:19, Bart Van Assche wrote:
> On 12/17/19 12:56 AM, cang@...eaurora.org wrote:
>> 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.
> 
> Hi Can,
> 
> Since ufs-bsg is not a platform device I think it would be wrong to
> model ufs-bsg devices as platform devices.
> 
> Please have a look at the bus_register() and bus_unregister()
> functions as Greg KH asked. Using the bus abstraction is not that
> hard. An example is e.g. available in the scsi_debug driver, namely
> the pseudo_lld_bus.
> 
> Thanks,
> 
> Bart.

Hi Bart,

Yes, I am talking the same here. Since platform device is not an option
for ufs-bsg, to make it a plain device we would need to do 
bus_register()
and bus_unregister(). And also do device_initialize() and device_add().

Thanks,
Can Guo.