linux-kernel - Re: [PATCH 2/6] fpga: manager: don't use drvdata in common fpga code

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Date:   Thu, 29 Mar 2018 13:26:39 -0500
From:   Alan Tull <atull@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Moritz Fischer <mdf@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [PATCH 2/6] fpga: manager: don't use drvdata in common fpga code

On Thu, Mar 29, 2018 at 12:03 PM, Greg KH <gregkh@...uxfoundation.org> wrote:

Hi Greg,

> On Thu, Mar 29, 2018 at 08:36:54AM -0700, Moritz Fischer wrote:
>> From: Alan Tull <atull@...nel.org>
>>
>> Change fpga_mgr_register to not set or use drvdata.
>>
>> Change the register/unregister function parameters to take the mgr
>> struct:
>> * int fpga_mgr_register(struct fpga_manager *mgr);
>> * void fpga_mgr_unregister(struct fpga_manager *mgr);
>>
>> Change the drivers that call fpga_mgr_register to alloc the struct
>> fpga_manager (using devm_kzalloc) and partly fill it, adding name,
>> ops, parent device, and priv.
>>
>> The rationale is that setting drvdata is fine for DT based devices
>> that will have one manager, bridge, or region per platform device.
>> However PCIe based devices may have multiple FPGA mgr/bridge/regions
>> under one PCIe device.  Without these changes, the PCIe solution has
>> to create an extra device for each child mgr/bridge/region to hold
>> drvdata.
>>
>> Signed-off-by: Alan Tull <atull@...nel.org>
>> Reported-by: Jiuyue Ma <majiuyue@...wei.com>
>> Signed-off-by: Moritz Fischer <mdf@...nel.org>
>> ---
>>  Documentation/fpga/fpga-mgr.txt  | 24 +++++++++++++++++-------
>>  drivers/fpga/altera-cvp.c        | 18 ++++++++++++++----
>>  drivers/fpga/altera-pr-ip-core.c | 17 +++++++++++++++--
>>  drivers/fpga/altera-ps-spi.c     | 18 +++++++++++++++---
>>  drivers/fpga/fpga-mgr.c          | 39 ++++++++++++++-------------------------
>>  drivers/fpga/ice40-spi.c         | 20 ++++++++++++++++----
>>  drivers/fpga/socfpga-a10.c       | 16 +++++++++++++---
>>  drivers/fpga/socfpga.c           | 18 +++++++++++++++---
>>  drivers/fpga/ts73xx-fpga.c       | 18 +++++++++++++++---
>>  drivers/fpga/xilinx-spi.c        | 18 +++++++++++++++---
>>  drivers/fpga/zynq-fpga.c         | 16 +++++++++++++---
>>  include/linux/fpga/fpga-mgr.h    |  8 ++++----
>>  12 files changed, 166 insertions(+), 64 deletions(-)
>>
>> diff --git a/Documentation/fpga/fpga-mgr.txt b/Documentation/fpga/fpga-mgr.txt
>> index cc6413ed6fc9..3cea6b57c156 100644
>> --- a/Documentation/fpga/fpga-mgr.txt
>> +++ b/Documentation/fpga/fpga-mgr.txt
>> @@ -67,11 +67,9 @@ fpga_mgr_unlock when done programming the FPGA.
>>  To register or unregister the low level FPGA-specific driver:
>>  -------------------------------------------------------------
>>
>> -     int fpga_mgr_register(struct device *dev, const char *name,
>> -                           const struct fpga_manager_ops *mops,
>> -                           void *priv);
>> +     int fpga_mgr_register(struct fpga_manager *mgr);
>>
>> -     void fpga_mgr_unregister(struct device *dev);
>> +     void fpga_mgr_unregister(struct fpga_manager *mgr);
>>
>>  Use of these two functions is described below in "How To Support a new FPGA
>>  device."
>> @@ -148,8 +146,13 @@ static int socfpga_fpga_probe(struct platform_device *pdev)
>>  {
>>       struct device *dev = &pdev->dev;
>>       struct socfpga_fpga_priv *priv;
>> +     struct fpga_manager *mgr;
>>       int ret;
>>
>> +     mgr = devm_kzalloc(dev, sizeof(*mgr), GFP_KERNEL);
>> +     if (!mgr)
>> +             return -ENOMEM;
>
> This feels odd to have to do for every driver.  Why can't the fpga core
> handle this all for you?
>
>
>> +
>>       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>>       if (!priv)
>>               return -ENOMEM;
>> @@ -157,13 +160,20 @@ static int socfpga_fpga_probe(struct platform_device *pdev)
>>       /* ... do ioremaps, get interrupts, etc. and save
>>          them in priv... */
>>
>> -     return fpga_mgr_register(dev, "Altera SOCFPGA FPGA Manager",
>> -                              &socfpga_fpga_ops, priv);
>
> Why can't this be:
>         fpga_mgr_create(...)
> that returns the correct structure?  That way each driver always gets
> the proper things set (you don't have to remember and audit each driver
> to ensure they do it all correctly), and all is good?
>
> That should make this a lot simpler to use, and change.

Are you suggesting something like this?

-       return fpga_mgr_register(dev, "Altera SOCFPGA FPGA Manager",
-                                &socfpga_fpga_ops, priv);
+       mgr = fpga_mgr_create(dev, "Altera SOCFPGA FPGA Manager",
+                               &socfpga_fpga_ops, priv);
+
+       platform_set_drvdata(pdev, mgr);
+
+       return fpga_mgr_register(mgr);

That would be straightforward and if there are more fields to fill in
in the future, we can still do that before calling fpga_mgr_register.

Alan

>
> thanks,
>
> greg k-h