linux-kernel - Re: Another approach of UFSHPB

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Date:   Mon, 25 May 2020 14:40:53 +0900
From:   Daejun Park <daejun7.park@...sung.com>
To:     Bart Van Assche <bvanassche@....org>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Avri Altman <Avri.Altman@....com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     ALIM AKHTAR <alim.akhtar@...sung.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        Zang Leigang <zangleigang@...ilicon.com>,
        Avi Shchislowski <Avi.Shchislowski@....com>,
        Bean Huo <beanhuo@...ron.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        MOHAMMED RAFIQ KAMAL BASHA <md.rafiq@...sung.com>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        Daejun Park <daejun7.park@...sung.com>
Subject: Re: Another approach of UFSHPB

I am Daejun Park who is working to patch HPB driver.
Thank you for your comment, and the following is our answer.

> Splitting the UFS driver into multiple modules would be great if the
> interface between these modules can be kept small and elegant. However,
> I'm not sure that this approach should be based on Linux device driver
> bus concept. Devices can be unbound at any time from their driver by
> writing into the "unbind" sysfs attribute. I don't think we want the UFS
> core functionality ever to be unbound while any other UFS functionality
> is still active. Has it been considered to implement each feature as a
> loadable module without relying on the bus model? The existing kernel
> module infrastructure already prevents to unload modules (e.g. the UFS
> core) that are in use by a kernel module that depends on it (e.g. UFS HPB).

The HPB driver is close to the UFS core function, but it is not essential
for operating UFS device. With reference to this article
(https://lwn.net/Articles/645810/), we implemented extended UFS-feature
as bus model. Because the HPB driver consumes the user's main memory, it should
support bind / unbind functionality as needed. We implemented the HPB driver 
can be unbind / unload on runtime.

> What will happen if a feature module is unloaded (e.g. HPB) while I/O is
> ongoing that relies on HPB?

In the HPB driver, it checks whether the HPB can be unload / unbind through
the reference counter. Therefore, there is no problem that the driver is 
unloaded / unbind when there is I/O related to HPB.

> Should these parameters be per module or per UFS device?

I think it is necessary to take parameters for each module. 
This is because each extended UFS-feature module has different functions
and may require different parameters.

Thanks,

Daejun Park.