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

[Bart Van Assche <bvanassche@acm.org>]

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.