Date:   Tue, 12 Oct 2021 15:56:49 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Russ Weight <russell.h.weight@...el.com>
Cc:     Tom Rix <trix@...hat.com>, mdf@...nel.org,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org,
        lgoncalv@...hat.com, hao.wu@...el.com, matthew.gerlach@...el.com
Subject: Re: [PATCH v17 0/5] FPGA Image Load (previously Security Manager)

On Tue, Oct 12, 2021 at 03:47:52PM +0800, Xu Yilun wrote:
> On Mon, Oct 11, 2021 at 06:00:16PM -0700, Russ Weight wrote:
> > 
> > 
> > On 10/11/21 5:35 AM, Tom Rix wrote:
> > >
> > > On 10/10/21 6:41 PM, Xu Yilun wrote:
> > >> On Sat, Oct 09, 2021 at 05:11:20AM -0700, Tom Rix wrote:
> > >>> On 10/9/21 1:08 AM, Xu Yilun wrote:
> > >>>> On Wed, Sep 29, 2021 at 04:00:20PM -0700, Russ Weight wrote:
> > >>>>> The FPGA Image Load framework provides an API to upload image
> > >>>>> files to an FPGA device. Image files are self-describing. They could
> > >>>>> contain FPGA images, BMC images, Root Entry Hashes, or other device
> > >>>>> specific files. It is up to the lower-level device driver and the
> > >>>>> target device to authenticate and disposition the file data.
> > >>>> I've reconsider the FPGA persistent image update again, and think we
> > >>>> may include it in FPGA manager framework.
> > >>>>
> > >>>> Sorry I raised this topic again when it is already at patch v17, but now
> > >>>> I need to consider more seriously than before.
> > >>>>
> > >>>> We have consensus the FPGA persistent image update is just like a normal
> > >>>> firmware update which finally writes the nvmem like flash or eeprom,
> > >>>> while the current FPGA manager deals with the active FPGA region update
> > >>>> and re-activation. Could we just expand the FPGA manager and let it handle
> > >>>> the nvmem update as well? Many FPGA cards have nvmem and downloaders
> > >>>> supports updating both FPGA region and nvmem.
> > The fpga-image-load driver is actually just a data transfer. The class
> 
> IMHO, The fpga-mgr dev is also a data transfer. The fpga-region dev is
> acting as the FPGA region admin responsible for gating, transfering and
> re-enumerating.
> 
> So my opinion is to add a new data transfer type and keep a unified process.
> 
> > driver has no knowledge about what the data is or where/if the data will
> > be stored.
> 
> The fpga-image-load driver knows the data will be stored in nvmem, while
> the fpga-mgr knows the data will be stored in FPGA cells. They may need
> to know the exact physical position to store, may not, depends on what the
> HW engines are.
> 
> > 
> > This functionality could, of course, be merged into the fpga-mgr. I did
> > a proof of concept of this a while back and we discussed the pros and cons.
> > See this email for a recap:
> > 
> > https://marc.info/?l=linux-fpga&m=161998085507374&w=2
> > 
> > Things have changed some with the evolution of the driver. The IOCTL
> > approach probably fits better than the sysfs implementation. At the time
> > it seemed that a merge would add unnecessary complexity without adding value.
> 
> I think at least developers don't have to go through 2 sets of software
> stacks which are of the same concept. And adding some new features like
> optionally threading or canceling data transfer are also good to FPGA
> region update. And the nvmem update could also be benifit from exsiting
> implementations like scatter-gather buffers, in-kernel firmware loading.
> 
> I try to explain myself according to each of your concern from that mail
> thread:
> 
> Purpose of the 2 updates
> ========================
> 
>   As I said before, I think they are both data transfer devices. FPGA
> region update gets extra support from fpga-region & fpga-bridge, and
> FPGA nvmem update could be a standalone fpga-mgr.
> 
> Extra APIs that are unique to nvmem update
> ==========================================
> 
>   cdev APIs for nvmem update:
>     Yes we need to expand the functionality so we need them.
> 
>   available_images, image_load APIs for loading nvmem content to FPGA
>   region:
>     These are features in later patchsets which are not submitted, but we
>     could talk about it in advance. I think this is actually a FPGA region
>     update from nvmem, it also requires gating, data loading (no SW transfer)
>     and re-enumeration, or a single command to image_load HW may result system
>     disordered. The FPGA framework now only supports update from in-kernel
>     user data, maybe we add support for update from nvmem later.
> 
>   fpga-mgr state extend:
>     I think it could be extended, The current states are not perfect,
>     adding something like IDLE or READY is just fine.
> 
>   fpga-mgr status extend:
>     Add general error definitions as needed. If there is some status
>     that is quite vendor specific, expose it in low-level driver.
> 
>   remaining-size:
>     Nice to have for all.
> 
> Threading the update
> ====================
> 
>   Also a good option for FPGA region update, maybe we also have a slow FPGA
>   reprogrammer?

Another thought is, could we implement the non-threading version
firstly, so there would be less change and faster to have the basic
functionality. But either is OK for me.

Thanks,
Yilun

> 
> Cancelling the update
> ====================
> 
>   Also a good option for FPGA region update if HW engine supports.
> 
> Thanks,
> Yilun
> 
> > 
> > >>>>
> > >>>> According to the patchset, the basic workflow of the 2 update types are
> > >>>> quite similar, get the data, prepare for the HW, write and complete.
> > >>>> They are already implemented in FPGA manager. We've discussed some
> > >>>> differences like threading or canceling the update, which are
> > >>>> not provided by FPGA manager but they may also nice to have for FPGA
> > >>>> region update. An FPGA region update may also last for a long time??
> > >>>> So I think having 2 sets of similar frameworks in FPGA is unnecessary.
> > >>>>
> > >>>> My quick mind is that we add some flags in struct fpga_mgr & struct
> > >>>> fpga_image_info to indicate the HW capability (support FPGA region
> > >>>> update or nvmem update or both) of the download engine and the provided
> > >>>> image type. Then the low-level driver knows how to download if it
> > >>>> supports both image types.An char device could be added for each fpga manager dev, providing the
> > >>>> user APIs for nvmem update. We may not use the char dev for FPGA region
> > >>>> update cause it changes the system HW devices and needs device hotplug
> > >>>> in FPGA region. We'd better leave it to FPGA region class, this is
> > >>>> another topic.
> > I'll give this some more thought and see if I can come up with some RFC
> > patches.
> > 
> > - Russ
> > >>>>
> > >>>> More discussion is appreciated.
> > >>> I also think fpga_mgr could be extended.
> > >>>
> > >>> In this patchset,
> > >>>
> > >>> https://lore.kernel.org/linux-fpga/20210625195849.837976-1-trix@redhat.com/
> > >>>
> > >>> A second, similar set of write ops was added to fpga_manger_ops,
> > >>>
> > >>> new bit/flag was added to fpga_image_info
> > >>>
> > >>> The intent was for dfl to add their specific ops to cover what is done in
> > >>> this patchset.
> > >> I think we don't have to add 2 ops for reconfig & reimage in framework,
> > >> the 2 processes are almost the same.
> > >>
> > >> Just add the _REIMAGE (or something else, NVMEM?) flag for
> > >> fpga_image_info, and low level drivers handle it as they do for other
> > >> flags.
> > >>
> > >> How do you think?
> > >
> > > A single set is fine.
> > >
> > > A difficult part of is the length of  time to do the write. The existing write should be improved to use a worker thread.
> > >
> > > Tom
> > >
> > >>
> > >> Thanks,
> > >> Yilun
> > >>
> > >>> Any other driver would do similar.
> > >>>
> > >>> Is this close to what you are thinking ?
> > >>>
> > >>> Tom
> > >>>
> > >>>> Thanks,
> > >>>> Yilun
> > >>>>
> > >

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