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

[Wu Hao <hao.wu@intel.com>]

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@kernel.org> wrote:
> > On Wed, Apr 5, 2017 at 6:40 AM, Wu, Hao <hao.wu@intel.com> 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?

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.

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.

Thanks
Hao

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