Re: [PATCH v16 0/6] Device Tree support for FPGA programming

[Moritz Fischer]

Hi Alan,

On Thu, Feb 11, 2016 at 2:17 PM, atull <atull@xxxxxxxxxxxxxxxxxxxxx> wrote:

>> > > I looked into it further and now I've got a solution for this issue
>> > > that I can post soon.  I can stop using the DT overlay configfs
>> > > interface and add a sysfs file for applying an overlay to an FPGA
>> > > region.  The FPGA region implementation will see the overlay before it
>> > > becomes part of the live tree.  Then it can do the FPGA programming
>> > > and see that succeed before the child nodes become part of the live
>> > > tree.  If FPGA programming fails, the overlay will be rejected before
>> > > it becomes part of the live tree.  By the time 'firmware-name' and the
>> > > child nodes show up in the live tree, they will be post-configuration
>> > > information.

I agree this would be a very nice interface, but Rob is right, having
two different
interfaces to load device-trees is probably bad in general.

>> Yes.  If any handler returns error, the overlay doesn't go into the
>> main tree.  Handler type to be registed could be:
>>
>>   int pre_add_handler(struct device_node *overlay,
>>                       struct device_node *target)
>
> And a third parameter of some flags to indicate whether the
> overlay is being added or removed.

Looks good to me.

>> That gives us the overlay after it's been unflattened and phandles
>> resolved and the node that it was targeted to.  I was going to
>> need find_target_node() to be exported, but this avoids that.
>>
>> Registration could by compatible string, of match, or path.  Path
>> would be too rigid in my case, I'd want to register for compatible
>> "fpga-region"

Looks good to me. I think we're getting pretty close :)

Moritz