Re: [PATCH QEMU v2 3/5] Add a GPIO backend using libgpiod

[Philippe Mathieu-Daudé]

On 4/23/20 11:01 AM, Geert Uytterhoeven wrote:
> Add a GPIO controller backend, to connect virtual GPIOs on the guest to
> physical GPIOs on the host.  This allows the guest to control any
> external device connected to the physical GPIOs.
> 
> Features and limitations:
>   - The backend uses libgpiod on Linux,
>   - For now only GPIO outputs are supported,
>   - The number of GPIO lines mapped is limited to the number of GPIO
>     lines available on the virtual GPIO controller.
> 
> Future work:
>   - GPIO inputs,
>   - GPIO line configuration,
>   - Optimizations for controlling multiple GPIO lines at once,
>   - ...
> 
> Signed-off-by: Geert Uytterhoeven <address@hidden>
> ---
> v2:
>   - Drop vgpios and gpios parameters, and map the full gpiochip instead,
>   - Replace hardcoded PL061 instance by multiple dynamic instances,
>     registered through qemu_gpiodev_add().
> ---
>  MAINTAINERS              |  6 +++
>  backends/Makefile.objs   |  2 +
>  backends/gpiodev.c       | 94 ++++++++++++++++++++++++++++++++++++++++
>  configure                | 28 ++++++++++++
>  include/sysemu/gpiodev.h | 12 +++++
>  5 files changed, 142 insertions(+)
>  create mode 100644 backends/gpiodev.c
>  create mode 100644 include/sysemu/gpiodev.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e760f65270d29d5d..a70af47430083d14 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -607,6 +607,12 @@ F: include/hw/arm/digic.h
>  F: hw/*/digic*
>  F: include/hw/*/digic*
>  
> +GPIO device backend
> +M: Geert Uytterhoeven <address@hidden>
> +S: Supported
> +F: backends/gpiodev.c
> +F: include/sysemu/gpiodev.h
> +
>  Goldfish RTC
>  M: Anup Patel <address@hidden>
>  M: Alistair Francis <address@hidden>
> diff --git a/backends/Makefile.objs b/backends/Makefile.objs
> index 28a847cd571d96ed..ee658e797454119a 100644
> --- a/backends/Makefile.objs
> +++ b/backends/Makefile.objs
> @@ -21,3 +21,5 @@ common-obj-$(CONFIG_LINUX) += hostmem-memfd.o
>  common-obj-$(CONFIG_GIO) += dbus-vmstate.o
>  dbus-vmstate.o-cflags = $(GIO_CFLAGS)
>  dbus-vmstate.o-libs = $(GIO_LIBS)
> +
> +common-obj-$(CONFIG_GPIODEV) += gpiodev.o
> diff --git a/backends/gpiodev.c b/backends/gpiodev.c
> new file mode 100644
> index 0000000000000000..df1bd0113c7b2985
> --- /dev/null
> +++ b/backends/gpiodev.c
> @@ -0,0 +1,94 @@
> +/*
> + * QEMU GPIO Backend
> + *
> + * Copyright (C) 2018-2020 Glider bv
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include <errno.h>

<errno.h> probably not needed.

> +#include <gpiod.h>

Please move this one...

> +
> +#include "qemu/osdep.h"
> +#include "qemu/config-file.h"
> +#include "qemu/cutils.h"
> +#include "qemu/error-report.h"
> +#include "qemu/module.h"
> +#include "qemu/option.h"
> +#include "qapi/error.h"
> +
> +#include "sysemu/gpiodev.h"
> +
> +#include "hw/irq.h"
> +#include "hw/qdev-core.h"

... here:

#include <gpiod.h>

> +
> +static void gpiodev_irq_handler(void *opaque, int n, int level)
> +{
> +    struct gpiod_line *line = opaque;
> +    int status;
> +
> +    status = gpiod_line_set_value(line, level);
> +    if (status < 0) {
> +        struct gpiod_chip *chip = gpiod_line_get_chip(line);
> +
> +        error_report("%s/%s: Cannot set GPIO line %u: %s",
> +                     gpiod_chip_name(chip), gpiod_chip_label(chip),
> +                     gpiod_line_offset(line), strerror(errno));
> +    }
> +}
> +
> +static int gpiodev_map_line(DeviceState *dev, struct gpiod_chip *chip,
> +                            unsigned int gpio, Error **errp)
> +{
> +    struct gpiod_line *line;
> +    qemu_irq irq;
> +    int status;
> +
> +    line = gpiod_chip_get_line(chip, gpio);
> +    if (!line) {
> +        error_setg(errp, "Cannot obtain GPIO line %u: %s", gpio,
> +                   strerror(errno));
> +        return -1;
> +    }
> +
> +    status = gpiod_line_request_output(line, "qemu", 0);
> +    if (status < 0) {
> +        error_setg(errp, "Cannot request GPIO line %u for output: %s", gpio,
> +                   strerror(errno));
> +        return status;
> +    }
> +
> +    irq = qemu_allocate_irq(gpiodev_irq_handler, line, 0);
> +    qdev_connect_gpio_out(dev, gpio, irq);
> +    return 0;
> +}
> +
> +void qemu_gpiodev_add(DeviceState *dev, const char *name, unsigned int 
> maxgpio,
> +                      Error **errp)
> +{
> +    struct gpiod_chip *chip;
> +    unsigned int i, n;
> +    int status;
> +
> +    chip = gpiod_chip_open_lookup(name);
> +    if (!chip) {
> +        error_setg(errp, "Cannot open GPIO chip %s: %s", name,
> +                   strerror(errno));
> +        return;
> +    }
> +
> +    n = gpiod_chip_num_lines(chip);
> +    if (n > maxgpio) {
> +        warn_report("Last %u GPIO line(s) will not be mapped", n - maxgpio);
> +        n = maxgpio;
> +    }
> +
> +    for (i = 0; i < n; i++) {
> +        status = gpiodev_map_line(dev, chip, i, errp);
> +        if (status < 0) {
> +            return;
> +        }
> +    }
> +
> +    info_report("Mapped %u GPIO lines", n);
> +}
> diff --git a/configure b/configure
> index 23b5e93752b6a259..8b133402ef727c8e 100755
> --- a/configure
> +++ b/configure
> @@ -509,6 +509,7 @@ libpmem=""
>  default_devices="yes"
>  plugins="no"
>  fuzzing="no"
> +gpio=""

Maybe name this feature 'libgpiod'?

>  
>  supported_cpu="no"
>  supported_os="no"
> @@ -1601,6 +1602,10 @@ for opt do
>    ;;
>    --gdb=*) gdb_bin="$optarg"
>    ;;
> +  --disable-gpio) gpio="no"
> +  ;;
> +  --enable-gpio) gpio="yes"

Ditto: --enable-libgpiod, because else it seems rather confusing.

> +  ;;
>    *)
>        echo "ERROR: unknown option $opt"
>        echo "Try '$0 --help' for more information"
> @@ -1894,6 +1899,7 @@ disabled with --disable-FEATURE, default is enabled if 
> available:
>    debug-mutex     mutex debugging support
>    libpmem         libpmem support
>    xkbcommon       xkbcommon support
> +  gpio            gpio support
>  
>  NOTE: The object files are built at the place where configure is launched
>  EOF
> @@ -6250,6 +6256,23 @@ case "$slirp" in
>      ;;
>  esac
>  
> +##########################################
> +# check for libgpiod
> +
> +if test "$gpio" != "no"; then
> +    if $pkg_config --exists "libgpiod"; then
> +        gpio="yes"
> +        libgpiod_libs=$($pkg_config --libs libgpiod)
> +        libgpiod_cflags=$($pkg_config --cflags libgpiod)
> +        libs_softmmu="$libs_softmmu $libgpiod_libs"
> +        QEMU_CFLAGS="$QEMU_CFLAGS $libgpiod_cflags"
> +    else
> +        if test "$gpio" = "yes" ; then
> +            feature_not_found "gpio" "Install libgpiod"
> +        fi
> +        gpio="no"
> +    fi
> +fi
>  
>  ##########################################
>  # End of CC checks
> @@ -6733,6 +6756,7 @@ echo "default devices   $default_devices"
>  echo "plugin support    $plugins"
>  echo "fuzzing support   $fuzzing"
>  echo "gdb               $gdb_bin"
> +echo "gpio support      $gpio"
>  
>  if test "$supported_cpu" = "no"; then
>      echo
> @@ -7614,6 +7638,10 @@ if test -n "$gdb_bin" ; then
>      echo "HAVE_GDB_BIN=$gdb_bin" >> $config_host_mak
>  fi
>  
> +if test "$gpio" = "yes" ; then
> +  echo "CONFIG_GPIODEV=y" >> $config_host_mak
> +fi
> +
>  if test "$tcg_interpreter" = "yes"; then
>    QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
>  elif test "$ARCH" = "sparc64" ; then
> diff --git a/include/sysemu/gpiodev.h b/include/sysemu/gpiodev.h
> new file mode 100644
> index 0000000000000000..bedd141001245207
> --- /dev/null
> +++ b/include/sysemu/gpiodev.h
> @@ -0,0 +1,12 @@
> +/*
> + * QEMU GPIO Backend
> + *
> + * Copyright (C) 2018-2020 Glider bv
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/typedefs.h"

"qemu/typedefs.h" not needed in includes.

> +
> +void qemu_gpiodev_add(DeviceState *dev, const char *name, unsigned int 
> maxgpio,
> +                      Error **errp);
>