Re: [PATCHv1 3/4] dt-bindings: fpga: add authenticate-fpga-config property

[Richard Gong]

On 11/16/20 8:24 PM, Xu Yilun wrote:
> On Mon, Nov 16, 2020 at 08:14:52AM -0600, Richard Gong wrote:
> > Hi Yilun,
> >
> > On 11/15/20 8:47 PM, Xu Yilun wrote:
> > > On Sun, Nov 15, 2020 at 11:21:06AM -0800, Moritz Fischer wrote:
> > > > Hi Richard,
> > > >
> > > > On Thu, Nov 12, 2020 at 12:06:42PM -0600, richard.gong@xxxxxxxxxxxxxxx wrote:
> > > > > From: Richard Gong <richard.gong@xxxxxxxxx>
> > > > >
> > > > > Add authenticate-fpga-config property for FPGA bitstream authentication.
> > > > >
> > > > > Signed-off-by: Richard Gong <richard.gong@xxxxxxxxx>
> > > > > ---
> > > > >   Documentation/devicetree/bindings/fpga/fpga-region.txt | 1 +
> > > > >   1 file changed, 1 insertion(+)
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > > > index e811cf8..7a512bc 100644
> > > > > --- a/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > > > +++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt
> > > > > @@ -187,6 +187,7 @@ Optional properties:
> > > > >   - external-fpga-config : boolean, set if the FPGA has already been configured
> > > > >   	prior to OS boot up.
> > > > >   - encrypted-fpga-config : boolean, set if the bitstream is encrypted
> > > > > +- authenticate-fpga-config : boolean, set if do bitstream authentication
> > > > It is unclear to me from the description whether this entails
> > > > authentication + reconfiguration or just authentication.
> > > >
> > > > If the latter is the case this should probably be described as such.
> > >
> > > If it is just authentication, do we still need to disable bridges in
> > > fpga_region_program_fpga?
> >
> > Yes.
> >
> > Except for the actual configuration of the device, the authentication
> > feature is the same as FPGA configuration.
>
> FPGA Bridges gate bus signals between a host and FPGA. So the FPGA
> region could not be accessed by host when doing configuration. But for
> this authentication, we are just writing the flash, we don't actually
> touch the FPGA soft logic. The host should still be able to operate on
> the old logic before reboot, is it?
Yes, it's feasible in theory but doesn't make much sense in practice. I 
prefer to keep fpga_region_program_fpga() unchanged.

Regards,
Richard

> Thanks,
> Yilun
>
> > Regards,
> > Richard
> >
> > > I'm wondering if the FPGA functionalities could still be working when
> > > the authenticating is ongoing, or when the authenticating is failed.
> >
> >
> >
> > > Thanks,
> > > Yilun
> > >
> > > > >   - region-unfreeze-timeout-us : The maximum time in microseconds to wait for
> > > > >   	bridges to successfully become enabled after the region has been
> > > > >   	programmed.
> > > > > --
> > > > > 2.7.4
> > > >
> > > > Thanks