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Subject: Re: [PATCHv1 3/4] dt-bindings: fpga: add authenticate-fpga-config
 property
To:     Xu Yilun <yilun.xu@intel.com>
Cc:     Moritz Fischer <mdf@kernel.org>, trix@redhat.com,
        linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org,
        dinguyen@kernel.org, sridhar.rajagopal@intel.com,
        Richard Gong <richard.gong@intel.com>
References: <1605204403-6663-1-git-send-email-richard.gong@linux.intel.com>
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From:   Richard Gong <richard.gong@linux.intel.com>
Message-ID: <1713a966-5b0f-4e65-70ee-793d09e53cec@linux.intel.com>
Date:   Wed, 18 Nov 2020 07:38:31 -0600
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On 11/17/20 11:47 PM, Xu Yilun wrote:
> On Tue, Nov 17, 2020 at 09:39:55AM -0600, Richard Gong wrote:
>>
>>
>> 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@linux.intel.com wrote:
>>>>>>> From: Richard Gong <richard.gong@intel.com>
>>>>>>>
>>>>>>> Add authenticate-fpga-config property for FPGA bitstream authentication.
>>>>>>>
>>>>>>> Signed-off-by: Richard Gong <richard.gong@intel.com>
>>>>>>> ---
>>>>>>>   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.
> 
> I'm thinking of the case of inband reprograming, that the QSPI flash
> controller itself is embedded in FPGA soft logic, then maybe host still
> need to access FPGA on authentication.

We can decide whether we should update fpga_region_program_fpga() 
function when you update for inband reprogramming case.

Regards,
Richard
> 
> Thanks,
> Yilun
> 
>>>>
>>>>> 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