linux-kernel - Re: [PATCH v2 0/4] rpmb subsystem, uapi and virtio-rpmb driver

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Date:   Wed, 06 Apr 2022 19:19:24 +0200
From:   Bean Huo <huobean@...il.com>
To:     Alex Bennée <alex.bennee@...aro.org>
Cc:     linux-kernel@...r.kernel.org, maxim.uvarov@...aro.org,
        joakim.bech@...aro.org, ulf.hansson@...aro.org,
        ilias.apalodimas@...aro.org, arnd@...aro.org,
        ruchika.gupta@...aro.org, tomas.winkler@...el.com,
        yang.huang@...el.com, bing.zhu@...el.com,
        Matti.Moell@...nsynergy.com, hmo@...nsynergy.com,
        linux-mmc@...r.kernel.org, linux-scsi@...r.kernel.org,
        bvanassche@....org
Subject: Re: [PATCH  v2 0/4] rpmb subsystem, uapi and virtio-rpmb driver

On Wed, 2022-04-06 at 12:22 +0100, Alex Bennée wrote:
> 
> Bean Huo <huobean@...il.com> writes:
> 
> > On Tue, 2022-04-05 at 16:43 +0100, Alex Bennée wrote:
> > > 
> > > Bean Huo <huobean@...il.com> writes:
> > > 
> > > > Hi Alex,
> > > > 
> > > > Thanks for this unified RPMB interface, I wanted to verify this
> > > > on
> > > > our
> > > > UFS, it seems you didn't add the UFS access interface in this
> > > > version 
> > > > from your userspace tools, right?
> > > 
> > > No I didn't but it should be easy enough to add some function
> > > pointer
> > > redirection everywhere one of the op_* functions calls a vrpmb_*
> > > function. Do you already have a UFS RPMB device driver?
> > > 
> > 
> > Hi Alex,
> > Thanks for your feedback.
> > 
> > We now access UFS RPMB through the RPMB LUN BSG device, RPMB is a
> > well-
> > known LU and we have a userspace tool to access it.
> > 
> > I see that if we're going to use your interface, "static struct
> > rpmb_ops" should be registered from a lower-level driver, for
> > example
> > in a UFS driver, yes there should be no problem with this
> > registration,
> > but I don't know with the current way Compared, what are the
> > advantages
> > to add a driver. maybe the main advantage is that we will have an
> > unified user space tool for RPMB. right?
> 
> Pretty much. The main issue for virtio-rpmb is it doesn't really fit
> neatly into the block stack because all it does is the RPMB part so a
> non-block orientate API makes sense.
> 
> Can you point be to where the UFS driver does it's current RPMB
> stuff?
> 

It's the SCSI BSG driver, in fact, we don't have a dedicated UFS RPMB
driver in the kernel. RPMB is a well known LU, we are using userspace
tools to issue SCSI commands directly to the UFS RPMB LU via ioctl()
from the BSG device node in the /dev/sg/ folder.

Here is the BSG part of the code in the userspace tools:

        io_hdr_v4.guard = 'Q';                                        
        io_hdr_v4.protocol = BSG_PROTOCOL_SCSI;                       
        io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_CMD;            
        io_hdr_v4.response = (__u64)sense_buffer;                     
        io_hdr_v4.max_response_len = SENSE_BUFF_LEN;                  
        io_hdr_v4.request_len = cmd_len;                              
        io_hdr_v4.request = (__u64)cdb;                               
                                                                                                                          
                                                                                 
        ioctl(fd, SG_IO, &io_hdr_v4))
...


> > 
> > Kind regards,
> > Bean
> 
>