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

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Date:   Fri, 30 Mar 2018 11:09:06 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Alan Tull <atull@...nel.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 01:26:39PM -0500, Alan Tull wrote:
> 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.

Or you can add another parameter to the fpga_mgr_create() call :)

Yes, that looks a lot better, thanks.

greg k-h