RE: [virtio-comment] Comments on RPMB config space chapter 5.2.14

["Huang, Yang" <yang.huang@intel.com>]

> -----Original Message-----
> From: Harald Mommer <hmo@opensynergy.com>
> Sent: Saturday, March 12, 2022 12:35 AM
> To: Huang, Yang <yang.huang@intel.com>; Alex BennÃe
> <alex.bennee@linaro.org>; virtio-comment@lists.oasis-open.org
> Cc: Lukasz Zawada <Lukasz.Zawada@opensynergy.com>
> Subject: Re: [virtio-comment] Comments on RPMB config space chapter
> 5.2.14
> 
> 
> On 11.03.22 17:02, Huang, Yang wrote:
> >
> >> 1.) We have an underlying physical RPMB device we would like to
> >> forward to a virtual machine via virtio RPMB. Looks like the physical
> >> device has a capacity of 256. 256 > 0x80. And 256 also does not fit
> >> in the u8 capacity of the
> > 256*128KB = 32MB RPMB. What's your flash, eMMC, UFS or NVMe?
> 
> UFS. I should still try to find out what exact chip is used on the board and try
> to confirm with the data sheet (if available) that the capacity of 256 we got
> from ioctl RPMB_IOC_CAP_CMD is indeed the correct one.
> Which means 32MB. just to rule out I'm not fooled by some obscure bug
> somewhere in the stack.
> 
> >> structure. Thinking now of cutting to 0x80 to fulfill the exact
> >> wording of the specification. Alternatively we might violate the
> >> specification and cut to 255 which is the biggest value still fitting
> >> in u8 capacity. But nothing of this is satisfying.
> >>
> >> 2.) Looking at the specification the maximum RPMB block count is 256.
> >> In our
> 
> I'm referring to the virtio specification as it is currently on latest master in
> https://github.com/oasis-tcs/virtio-spec.git.
> 
> 2.) is not about the total size of the RPMB device but about the max.
> allowed number of blocks to be read or written at a time in one chunk (config
> space max_wr_cnt and max_rd_cnt). While in the text 256B is still a valid
> value in the config space this value would not fit into the u8. Not the issue
> now but remarkable when we are already in clause 5.12.4.
> 

Note: The normative reference of this RPMB section is based-on eMMC Spec 5.1.