Re: [PATCH 11/16] fpga: intel: fme: add partial reconfiguration sub feature support

[Alan Tull]

On Thu, Apr 6, 2017 at 5:57 AM, Wu Hao <hao.wu@xxxxxxxxx> wrote:
> On Wed, Apr 05, 2017 at 10:39:05AM -0500, Alan Tull wrote:
>> On Wed, Apr 5, 2017 at 10:26 AM, Alan Tull <atull@xxxxxxxxxx> wrote:
>> > On Wed, Apr 5, 2017 at 6:40 AM, Wu, Hao <hao.wu@xxxxxxxxx> wrote:
>> >>> >> The  fpga_image_info struct started life as just image specific info,
>> >>> >> but I want it to go in the direction of including parameters needed to
>> >>> >> program it this specific time. Otherwise we are stuck having to keep
>> >>> >> adding parameters as our use of FPGA develops.  It probably could be
>> >>> >> documented better as 'information needed to program a FPGA image'
>> >>> >> rather than strictly 'information about this particular FPGA image'.
>> >>> >> My patch "fpga-mgr: pass parameters for loading fpga in image info"
>> >>> >> goes in this direction by having the buf, firmware name, or sg list
>> >>> >> passed in the info for the added fpga_mgr_load() function.  Actually I
>> >>> >> should probably simplify the API and get rid of fpga_mgr_buf_load,
>> >>> >> fpga_mgr_buf_load_sg, and fpga_mgr_firmware_load and require people to
>> >>> >> use fpga_mgr_load (passing all parameters in fpga_image_info).
>> >>> >>
>> >>> >
>> >>> > Make sense.
>> >>> >
>> >>> >> > It may be a
>> >>> >> > little confusing. One rough idea is that keep this info under fpga region
>> >>> >> > (maybe its private data), and pass the fpga-region to fpga_mgr_buf_load,
>> >>> >>
>> >>> >> Yes, keep this info in fpga-region.  When the region wants to program
>> >>> >> using fpga-mgr, add the region id to fpga_image_info.  I propose
>> >>> >> calling it region_id.
>> >>> >
>> >>> > Hm.. Do we need a function which moves info from region to image info?
>> >>>
>> >>> No, just code that sets that variable in the struct before calling the
>> >>> fpga_region_program_fpga function.
>> >>>
>> >>> >
>> >>> > Another idea is, add a priv to fpga_image_info, and use a common function
>> >>> > to pass the fpga_region's priv to fpga_image_info's priv before PR.
>> >>> > fpga-mgr then knows fpga_region priv info from the fpga_image_info.
>> >>> >
>> >>>
>> >>> Adding priv would make the interface for fpga-mgr non-uniform.  The point
>> >>> of having a fpga-mgr framework is that there
>> >>> is the potential of the upper layers working for different FPGA devices.
>> >>> If the interface for each FPGA device were different, that would then
>> >>> be broken.
>> >>>
>> >>
>> >> I mean drivers can register their own fpga-mgr ops, and handle priv of
>> >> fpga_image_info in driver specific way for pr (e.g write_init function).
>> >> We don't need to change the any upper layer interfaces.
>> >
>> > I'm trying to avoid driver specific ways of doing things.  Think of this
>> > all as a set of blocks and we want to be able to switch out individual
>> > blocks in the future.  It's future-proofing and also making code more
>> > generally usable.
>> >
>> > fpga_mgr_info is part of the interface for calls to fpga-mgr to do
>> > reprogramming.  My patchset will push it further in that direction
>> > as pointers to the image are added to fpga_mgr_info.
>> >
>> > Adding 'priv' to fpga_mgr_info makes that interface specific to a this driver.
>> > It's better to add a region_id variable to fpga_mgr_info that may not be used by
>> > all fpga-mgr drivers.  The current model is that a fpga-mgr driver checks
>> > fpga_mgr_info flags to see if its correct.  The fpga-mgr driver can check
>> > any other needed fpga_mgr_info variables and return error if the params
>> > look invalid.  And ignore any it doesn't need.
>> >
>> > I don't think priv belongs in fpga_image_info.  priv tends to be information
>> > for a specific instance of a driver that can have several instances.  priv
>> > usually stores a driver's memory mappings, interrupts, etc for that instance.
>> > It's called private info as it is info that other blocks don't need to know
>> > and don't get to look at.  It's private.  So priv as in interface strikes me as
>> > not private any more and is sort of a red flag.
>
> Thanks a lot for the details. It's more clear to me now. :)
>
>> >
>> > Alan
>>
>> Besides that, I see that region_id is needed both for the fme_pr and
>> for determining which port to disable/enable.  So adding it to the
>> fpga_image_info would allow the fpga-region to figure out which
>> bridge to control as well as pass it to the mgr.
>>
>
> Do we need to add an 'id' to fpga-bridge too?

You don't have to, but you could.  See below.

>
> Per my understanding this FME driver should create fpga-region for each
> accelerator, and make sure each fpga-region has correct region_id. When
> this fpga-region wants to be programmed by fpga-mgr, then it add this
> info to fpga_image_info, and fpga-mgr knows which region to program via
> this fpga_image_info.

The fpga_image_info is passed both to fpga-mgr and fpga-bridge.  So
both will get the region_id through the info.

>
> For each fpga-region, FME driver needs to create one fpga-bridge and link
> it to region's bridge_list. When fpga_region_program_fpga is invoked for
> PR. This fpga-bridge could be disabled before PR and re-enabled after PR
> automatically. If fpga-bridge contains this 'id' information, then driver
> knows which port to enable/disable to implement of the enable_set function
> under this fpga-bridge.

Could implement it either way: the bridge could either use the
bridge_id that has been passed to it in the info or code that creates
the bridge could create private data and pass it to
fpga_bridge_register().  But the bridge will have the id because it
will be passed in the info, so it's not really needed.

Alan

>
> Thanks
> Hao
>
>> >
>> >>
>> >> If you prefer the region_id for fpga_image_info, we can go with region_id
>> >> for sure. : )
>> >>
>> >> Thanks
>> >> Hao