Re: [PATCH] fpga: add simple userspace interface to trigger FPGA programming

[Alan Tull <atull@kernel.org>]

On Mon, Dec 4, 2017 at 9:43 AM, Thomas Petazzoni
<thomas.petazzoni@free-electrons.com> wrote:
> The current FPGA subsystem only allows programming the FPGA bitstream
> through Device Tree overlays. This assumes that the devices inside the
> FPGA are described through a Device Tree.
>
> However, some platforms have their FPGA connected to the main CPU over
> PCIe and the devices in the FPGA are therefore dynamically
> discoverable using the normal PCIe enumeration mechanisms. There is
> therefore no Device Tree overlay describing the devices in the
> FPGA. Furthermore, on my platform (an old SH7786), there is no Device
> Tree at all, as there is no support for Device Tree for this SoC.
>
> Adding a userspace interface to trigger the programming of the FPGA
> has already been requested in the past (see [1]) showing that there is
> a need for such a feature.
>
> This commit therefore introduces a very simple interface, in the form
> of a "load" sysfs file. Writing the name of the firmware file to
> program into the FPGA to this "load" file triggers the programming
> process.
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-July/443034.html
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Hi Thomas,

The problem I see with this is that it's allowing userspace to switch
out what's on the FPGA without controlling bridges and without
unloading drivers first.

Alan

> ---
>  Documentation/ABI/testing/sysfs-class-fpga-manager | 11 +++++++++
>  drivers/fpga/fpga-mgr.c                            | 28 ++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-class-fpga-manager b/Documentation/ABI/testing/sysfs-class-fpga-manager
> index 23056c532fdd..46785ad8b878 100644
> --- a/Documentation/ABI/testing/sysfs-class-fpga-manager
> +++ b/Documentation/ABI/testing/sysfs-class-fpga-manager
> @@ -35,3 +35,14 @@ Description: Read fpga manager state as a string.
>                 * write complete        = Doing post programming steps
>                 * write complete error  = Error while doing post programming
>                 * operating             = FPGA is programmed and operating
> +
> +What:          /sys/class/fpga_manager/<fpga>/load
> +Date:          December 2017
> +KernelVersion: 4.16
> +Contact:       Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> +
> +Description:   Program a bitstream firmware into the FPGA.
> +
> +               Writing the name of a firmware file into this "load"
> +               file will trigger the programming of the FPGA using
> +               that firmware.
> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
> index 188ffefa3cc3..1c7ca77c96c2 100644
> --- a/drivers/fpga/fpga-mgr.c
> +++ b/drivers/fpga/fpga-mgr.c
> @@ -351,12 +351,40 @@ static ssize_t state_show(struct device *dev,
>         return sprintf(buf, "%s\n", state_str[mgr->state]);
>  }
>
> +static ssize_t load_store(struct device *dev,
> +                         struct device_attribute *attr, const char *buf,
> +                         size_t count)
> +{
> +       struct fpga_manager *mgr = to_fpga_manager(dev);
> +       char *name;
> +       int ret;
> +
> +       if (count > 0 && buf[count - 1] == '\n')
> +               count--;
> +
> +       name = kstrndup(buf, count, GFP_KERNEL);
> +       if (!name)
> +               return -ENOSPC;
> +
> +       ret = fpga_mgr_firmware_load(mgr, NULL, name);
> +       if (ret < 0) {
> +               kfree(name);
> +               return ret;
> +       }
> +
> +       kfree(name);
> +
> +       return count;
> +}
> +
>  static DEVICE_ATTR_RO(name);
>  static DEVICE_ATTR_RO(state);
> +static DEVICE_ATTR_WO(load);
>
>  static struct attribute *fpga_mgr_attrs[] = {
>         &dev_attr_name.attr,
>         &dev_attr_state.attr,
> +       &dev_attr_load.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(fpga_mgr);
> --
> 2.13.6
>