On Tue, 24 Jan 2023 17:51:55 -0600 Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > On Tue, Jan 24, 2023 at 12:43:15PM +0000, Jonathan Cameron wrote: > > On Mon, 23 Jan 2023 11:20:00 +0100 > > Lukas Wunner <lukas@xxxxxxxxx> wrote: > > > > > An upcoming user of DOE is CMA (Component Measurement and Authentication, > > > PCIe r6.0 sec 6.31). > > > > > > It builds on SPDM (Security Protocol and Data Model): > > > https://www.dmtf.org/dsp/DSP0274 > > > > > > SPDM message sizes are not always a multiple of dwords. To transport > > > them over DOE without using bounce buffers, allow sending requests and > > > receiving responses whose final dword is only partially populated. > > > > > > Tested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > > > Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx> > > > Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > > Ah. This... > > > > I can't immediately find the original discussion thread, but I'm fairly > > sure we had a version of the DOE code that did this (maybe we just > > discussed doing it and never had code...) > > > > IIRC, at the time feedback was strongly in favour of making > > the handling of non dword payloads a problem for the caller (e.g. PCI/CMA) > > not the DOE core, mainly so that we could keep the layering simple. > > DOE part of PCI spec says DWORD multiples only, CMA has non dword > > entries. > > I can't remember, but I might have been the voice in favor of making > it the caller's problem. Your argument about dealing with it here > makes a lot of sense, and I'm OK with it, but I *would* like to add > some text to the commit log and comments in the code about what is > happening here. Otherwise there's an unexplained disconnect between > the DWORD spec language and the byte-oriented code. Absolutely agree. Calling out why we have a mismatch with the specification will avoid a bunch of head scratching in the future! > > > Personally I'm fully in favour of making our lives easier and handling > > this at the DOE layer! The CMA padding code is nasty as we have to deal > > with caching just the right bits of the payload for the running hashes. > > With it at this layer I'd imagine that code gets much simpler > > > > Assuming resolution to Ira's question on endianness is resolved. > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
