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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>
 <1605204403-6663-4-git-send-email-richard.gong@linux.intel.com>
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 <20201116024758.GA6810@yilunxu-OptiPlex-7050>
 <d83b37c2-2baa-b366-8ca4-bb2924bcd4f9@linux.intel.com>
 <20201117022453.GA12837@yilunxu-OptiPlex-7050>
From:   Richard Gong <richard.gong@linux.intel.com>
Message-ID: <e9492bbf-f3c5-41a7-0a08-8de142700880@linux.intel.com>
Date:   Tue, 17 Nov 2020 09:39:55 -0600
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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.

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