Re: [PATCH v2 02/16] fpga: bridge: support getting bridge from device

Moritz Fischer
2017-05-08T21:56:04Z

Hi Alan,

On Mon, May 8, 2017 at 2:20 PM, Alan Tull <atull@kernel.org> wrote:
> On Mon, May 8, 2017 at 4:11 PM, Moritz Fischer <mdf@kernel.org> wrote:
>> Hi Alan,
>>
>> On Mon, May 8, 2017 at 2:02 PM, Alan Tull <atull@kernel.org> wrote:
>>> On Mon, May 8, 2017 at 3:52 PM, Moritz Fischer <mdf@kernel.org> wrote:
>>>> On Mon, May 8, 2017 at 1:44 PM, Alan Tull <atull@kernel.org> wrote:
>>>>> On Mon, May 8, 2017 at 3:44 AM, Wu, Hao <hao.wu@intel.com> wrote:
>>>>>>> On Wed, May 3, 2017 at 3:07 PM, Alan Tull <atull@kernel.org> wrote:
>>>>>>> > On Wed, May 3, 2017 at 6:58 AM, Wu Hao <hao.wu@intel.com> wrote:
>>>>>>> >> On Thu, Apr 20, 2017 at 09:09:47AM -0500, Alan Tull wrote:
>>>>>>> >>> Add two functions for getting the FPGA bridge from the device
>>>>>>> >>> rather than device tree node. This is to enable writing code
>>>>>>> >>> that will support using FPGA bridges without device tree.
>>>>>>> >>> Rename one old function to make it clear that it is device
>>>>>>> >>> tree-ish. This leaves us with 3 functions for getting a bridge:
>>>>>>> >>>
>>>>>>> >>> * fpga_bridge_get
>>>>>>> >>> Get the bridge given the device.
>>>>>>> >>>
>>>>>>> >>> * fpga_bridges_get_to_list
>>>>>>> >>> Given the device, get the bridge and add it to a list.
>>>>>>> >>>
>>>>>>> >>> * of_fpga_bridges_get_to_list
>>>>>>> >>> Renamed from priviously existing fpga_bridges_get_to_list.
>>>>>>> >>> Given the device node, get the bridge and add it to a list.
>>>>>>> >>>
>>>>>>> >>
>>>>>>> >> Hi Alan
>>>>>>> >>
>>>>>>> >> Thanks a lot for providing this patch set for non device tree support. :)
>>>>>>> >> Actually I am reworking the Intel FPGA device drivers based on this patch
>>>>>>> >> set, and I find some problems with the existing APIs including fpga bridge
>>>>>>> >> and manager. My idea is to create all fpga bridges/regions/manager under
>>>>>>> >> the same platform device (FME), it allows FME driver to establish the
>>>>>>> >> relationship for the bridges/regions/managers it creates in an easy way.
>>>>>>> >> But I found current fpga class API doesn't support this very well.
>>>>>>> >> e.g fpga_bridge_get/get_to_list only accept parent device as the input
>>>>>>> >> parameter, but it doesn't work if we have multiple bridges (and
>>>>>>> >> regions/manager) under the same platform device. fpga_mgr has similar
>>>>>>> >> issue, but fpga_region APIs work better, as they accept fpga_region as
>>>>>>> >> parameter not the shared parent device.
>>>>>>> >
>>>>>>> > That's good feedback. I can post a couple patches that apply on top
>>>>>>> > of that patchset to add the APIs you need.
>>>>>>> >
>>>>>>> > Probably what I'll do is add
>>>>>>> >
>>>>>>> > struct fpga_manager *fpga_mgr_get(struct fpga_manager *mgr);
>>>>>>> >
>>>>>>> > And rename fpga_bridge_get() to fpga_bridge_dev_get() and add the
>>>>>>> following:
>>>>>>> >
>>>>>>> > struct fpga_bridge *fpga_bridge_get(struct fpga_bridge *br,
>>>>>>> > struct fpga_image_info *info);
>>>>>>> >
>>>>>>> > int of_fpga_bridge_get_to_list(struct fpga_bridge *br,
>>>>>>> > struct fpga_image_info *info,
>>>>>>> > struct list_head *bridge_list);
>>>>>>> >
>>>>>>> > Working on it now.
>>>>>>> >
>>>>>>> >>
>>>>>>> >> Do you think if having multiple fpga-* under one parent device is in the
>>>>>>> >> right direction?
>>>>>>> >
>>>>>>> > That should be fine as long as it's coded with an eye on making things
>>>>>>> > reusable and seeing beyond the current project. Just thinking of the
>>>>>>> > future and of what can be of general usefulness for others. And there
>>>>>>> > will be others interested in reusing this.
>>>>>>> >
>>>>>>> > Alan
>>>>>>>
>>>>>>> Actually, I don't think you will need the additional APIs we were
>>>>>>> just discussing after all. What you have is a multifunction device
>>>>>>> (single piece of hardware, multi functions such as in drivers/mfd).
>>>>>>> It will have child devices for the mgr, bridges, and regions. When
>>>>>>> registering the mgr and bridges you will need to allocate child
>>>>>>> devices and use them to create the mgr and bridges.
>>>>>>>
>>>>>>> Alan
>>>>>>
>>>>>> Hi Alan
>>>>>>
>>>>>> I tried to create child devices as the parent device for the mgr and
>>>>>> bridges in fme platform driver module. If only creates the device without
>>>>>> driver, it doesn't work as try_module_get(dev->parent->driver->owner)
>>>>>> always failed in mgr_get and bridge_get functions.
>>>>>
>>>>> I tried it and it wasn't hard.
>>>>>
>>>>> Each mgr or bridge driver should be a separate file which registers
>>>>> its driver using 'module_platform_driver". That way the drivers are
>>>>> registered with the kernel in a normal fashion. The thing we want
>>>>> here is to not bypass the kernel driver model.
>>>>>
>>>>> You'll need to keep the platform_device pointers in private data somewhere.
>>>>>
>>>>> For each child platform device, do a platform_device_alloc and
>>>>> platform_device_add.
>>>>>
>>>>> Then to get the manager, you can do
>>>>>
>>>>> mgr = fpga_mgr_get(&priv->mgr_pdev->dev);
>>>>>
>>>>> If this is in your probe function, you can use -EPROBE_DEFER if
>>>>> platform_device_alloc or fpga_mgr_get fail. Then you could destroy
>>>>> whatever you've created and return -EPROBE_DEFER to wait for the
>>>>> drivers you need to be registered and ready for devices to be added.
>>>>>
>>>>>>
>>>>>> If it creates platform devices as child devices, and introduce new platform
>>>>>> device drivers for bridge and mgr, then it will be difficult to establish the
>>>>>> relationship for region/mgr/bridges (e.g when should region->mgr be
>>>>>> configured and cleared, as mgr is created/destroyed when mgr parent
>>>>>> device platform driver module is loaded/unload), and it maybe not really
>>>>>> necessary to introduce more different driver modules here.
>>>>>
>>>>> It should be pretty easy to create/destroy child devices as shown
>>>>> above. The kernel does this all the time.
>>>>>
>>>>>>
>>>>>> But if it allows multiple fpga-* created under one device in one device
>>>>>> driver, it will be much easier to avoid above problems. So I asked if it
>>>>>> is possible to create multiple fpga-* under one parent device,
>>>>>
>>>>> I think it's fine for your FME to create child platform devices. It's
>>>>> similar to a mfd, but the mfd framework hides the platform devices
>>>>> from the module that creates them, unfortunately.
>>>>>
>>>>>> I feel
>>>>>> this will not impact to current fpga drivers a lot, but provide more
>>>>>> flexibility for drivers to use fpga-region/bridge/manager to create
>>>>>> the topology in a device specific way, especially for non device
>>>>>> tree case.
>>>>>>
>>>>>
>>>>> I would like to see most of this code as FME enumeration code + a mgr
>>>>> driver + a bridge driver + a region driver. If the FME and the
>>>>> enumeration code can be separate files, so much the better for general
>>>>> usability.
>>>>>
>>>>> The enumeration code can build a set of regions by doing something like this:
>>>>> 1. figure out what type of mgr and bridges your hardware FME has.
>>>>> 2. do platform_device_alloc and platform_device_add to create the mgr
>>>>> device, save a pointer to its platform_device in your FME driver's
>>>>> private data.
>>>>> 2. For each port, create a region and a bridge device. Save the
>>>>> region's platform device or struct in a list in your FME driver's
>>>>> priv.
>>>>> 3. then you can create the sub function devices.
>>>>
>>>> The above sounds like a poster-child application for MFD. If you do it
>>>> in a clever
>>>> way (i.e. write your platform drivers in a reusable way) you might be able to
>>>> just reuse them on your next generation.
>>>
>>> Yes, I played with that with some test code. I wrote some test code
>>> that allocates dummy mgr and bridge devices using mfd_add_devices().
>>> I didn't see any way of getting access to the devices after creating
>>> them. Maybe I'm missing something. Neither the dev nor the
>>> platform_device is saved in the cell struct.
>>
>> Currently working on some MFD stuff for an RTC, which device are you
>> trying to get to?
>>
>> The parent from subdevice (fpga mgr?) you can get by something like:
>>
>> foo_fpga_mgr_probe(struct platform_device *pdev)
>> {
>> struct foo_parent *parent = dev_get_drvdata(dev->parent);
>> }
>>
>> Or are you talking about the other way round (i.e. get access to children from
>> parent device) ?
>
> That's it.
>
>> Which functionality would that achieve?
>
> Suppose someone (non-DT case) is enumerating some hardware in the FPGA
> that includes a mgr and some bridges. So they create the mgr device.
> Then for each bridge and they want to create a bridge device and a
> region device and let the region know what mgr and bridge to use. The
> main enumerating device keeps track of all these regions so if stuff
> gets unloaded, it can destroy it all properly.

Ok that might be tougher :( Don't have a solution for that up my sleeve ;-)

Cheers,
Moritz