Re: [PATCH] fpga: mgr: Use devicetree /alias to assign FPGA IDs

From: Alan Tull <atull@kernel.org>
To: Brandon Maier <brandon.maier@rockwellcollins.com>
Cc: Moritz Fischer <mdf@kernel.org>,
	linux-fpga@vger.kernel.org, clayton.shotwell@rockwellcollins.com
Subject: Re: [PATCH] fpga: mgr: Use devicetree /alias to assign FPGA IDs
Date: Mon, 15 Apr 2019 13:31:00 -0500	[thread overview]
Message-ID: <CANk1AXThTMyE0+z9_ncF=AsNxUMPtZ1Z-Yksj6Ms7OPqNNi=xQ@mail.gmail.com> (raw)
In-Reply-To: <20190411221109.173242-1-brandon.maier@rockwellcollins.com>

On Thu, Apr 11, 2019 at 5:12 PM Brandon Maier
<brandon.maier@rockwellcollins.com> wrote:

Hi Brandon,

Thanks!  This is useful.

>
> The fpga-mgr assigns device IDs based on the order each driver calls
> fpga_mgr_register(). This is fine for systems with one FPGA, but if
> multiple FPGAs are in use, the device ID can change as probe order
> changes across reboots or configuration changes.
>
> This makes it difficult to use the sysfs attributes, as the device path
> may change. Instead allow a static ID to be set by adding fpgaX props
> to the devicetree /aliases. Falling back to incrementing IDs if none are
> provided.
>
> This is based on the function rtc_device_get_id() in drivers/rtc/class.c
> (9d2b7e532da8 rtc: honor device tree /alias entries when assigning IDs).
>
> Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
Acked-by: Alan Tull <atull@kernel.org>

Alan

> ---
>  drivers/fpga/fpga-mgr.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
> index c3866816456a..d8b7e7a61117 100644
> --- a/drivers/fpga/fpga-mgr.c
> +++ b/drivers/fpga/fpga-mgr.c
> @@ -551,6 +551,26 @@ void fpga_mgr_unlock(struct fpga_manager *mgr)
>  }
>  EXPORT_SYMBOL_GPL(fpga_mgr_unlock);
>
> +static int fpga_mgr_get_id(struct device *dev)
> +{
> +       int of_id = -1, id = -1;
> +
> +       if (dev->of_node)
> +               of_id = of_alias_get_id(dev->of_node, "fpga");
> +
> +       if (of_id >= 0) {
> +               id = ida_simple_get(&fpga_mgr_ida, of_id, of_id + 1,
> +                                   GFP_KERNEL);
> +               if (id < 0)
> +                       dev_warn(dev, "/aliases ID %d not available\n", of_id);
> +       }
> +
> +       if (id < 0)
> +               id = ida_simple_get(&fpga_mgr_ida, 0, 0, GFP_KERNEL);
> +
> +       return id;
> +}
> +
>  /**
>   * fpga_mgr_create - create and initialize a FPGA manager struct
>   * @dev:       fpga manager device from pdev
> @@ -586,7 +606,7 @@ struct fpga_manager *fpga_mgr_create(struct device *dev, const char *name,
>         if (!mgr)
>                 return NULL;
>
> -       id = ida_simple_get(&fpga_mgr_ida, 0, 0, GFP_KERNEL);
> +       id = fpga_mgr_get_id(dev);
>         if (id < 0) {
>                 ret = id;
>                 goto error_kfree;
> --
> 2.20.1
>