Re: [RFC 7/8] fpga-region: add sysfs interface

From: Alan Tull
Date: Wed Feb 22 2017 - 11:59:25 EST

On Wed, Feb 22, 2017 at 10:44 AM, Moritz Fischer
<moritz.fischer@xxxxxxxxx> wrote:
> On Wed, Feb 22, 2017 at 8:33 AM, Alan Tull <delicious.quinoa@xxxxxxxxx> wrote:
>> On Tue, Feb 21, 2017 at 11:38 PM, Moritz Fischer
>> <moritz.fischer@xxxxxxxxx> wrote:
>> Hi Moritz,
>>> Hi all,
>>> On Tue, Feb 21, 2017 at 9:12 PM, Jason Gunthorpe
>>> <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>> On Tue, Feb 21, 2017 at 07:49:19PM -0800, Moritz Fischer wrote:
>>>>> fdt does this out of the box, too. So far I've seen nothing fdt
>>>>> couldn't do (or doesn't do let's rather say).
>>>> tlv/fdt/http headers are all essentially exactly the same
>>>> thing. Key/value pairs with various encoding schemes.
>>>> I don't think we don't need a tree of data, so fdt is overkill.
>>>> tlv is not substantially easier to parse correctly than the
>>>> structured plain text headers.. It is just in binary so it can
>>>> represent binary-ish things better.
>>> TLV Seems easy enough. To give an update, I played with fdt a bit to see
>>> how far I get in half an hour. I got bool / int / strings to work
>>> quite fast (~30mins).
>> Thanks for doing this fast piece of exploratory coding. It does
>> confirm that for Linux, using fdt is pretty straightforward here.
>> However...
>>> Please disregard the horrible hackyness of this ...
>>> For simplicity I stuck the header on top of my bitfile with:
>>> <snip>
>>> /dts-v1/;
>>> /{
>>> description = "Test";
>>> compressed = <0>;
>>> encrypted = <1>;
>>> };
>> I understand that this is a simplified example, but it looks a lot
>> like KVP which then gets compiled by dtc.
>> If we do KVP or TLV we get skip using dtc, which would be nice for non-dt
>> OS's using the same images.
> I used dtc for pure lazyness. Writing a blob to a file using libfdt is
> about as much
> code as parsing it.

Thanks for that clarification. I haven't used libfdt myself. That
takes care of the license issue I brought up below.

I have heard that MS is averse to using DT, but I'm not clear
about why other than that it isn't native to Windows already.


> Even with KVP or TLV you have some code that needs
> to encode / pack your header into a file.
> libfdt has an example that creates an empty tree. Write that to a file, done.
> 1: Create empty tree
> 2: fopen / fwrite, done
>> Also, the license of libfdt allows the use by proprietary
>> os's, but that's not true for dtc.
> Why would that be an issue, you don't need to link anything to run
> dtc. That being
> said as I pointed out above you don not have to actually use dtc if the values
> are known ahead of time (like in our case). What you'd get from using dtc is to
> encode arbitrary values (for the types supported).
> Cheers,
> Moritz