Date:   Sun, 20 Dec 2020 23:56:12 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 5/9] media: uvcvideo: Implement UVC_EXT_GPIO_UNIT

HI Laurent

Thanks for your review!

On Sun, Dec 20, 2020 at 5:49 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Tue, Dec 15, 2020 at 04:44:35PM +0100, Ricardo Ribalda wrote:
> > Some devices can implement a physical switch to disable the input of the
> > camera on demand. Think of it like an elegant privacy sticker.
> >
> > The system can read the status of the privacy switch via a GPIO.
> >
> > It is important to know the status of the switch, e.g. to notify the
> > user when the camera will produce black frames and a videochat
> > application is used.
> >
> > Since the uvc device is not aware of this pin (and it should't), we need
>
> s/should't/shouldn't/
>
> But I don't agree, if this is part of the camera, it should be
> implemented in the camera firmware. I understand that it's not possible
> (or desirable) with the hardware architecture you're dealing with
> though. How about
>
> "In some systems, the GPIO is connected to main SoC instead of the
> camera controller, with the connected reported by the system firmware
> (ACPI or DT). In that case, the UVC device isn't aware of the GPIO. We
> need to implement a virtual entity to handle the GPIO fully on the
> driver side.
>
> For example, for ACPI-based systems, the GPIO is reported in the USB
> device object:"
>
> > to implement a virtual entity that can interact with such pin.
> >
> > The location of the GPIO is specified via acpi or DT. on the usb device Eg:
> >
> >   Scope (\_SB.PCI0.XHCI.RHUB.HS07)
> >   {
> >
> >         /.../
> >
> >     Name (_CRS, ResourceTemplate ()  // _CRS: Current Resource Settings
> >     {
> >         GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly,
> >             "\\_SB.PCI0.GPIO", 0x00, ResourceConsumer, ,
> >             )
> >             {   // Pin list
> >                 0x0064
> >             }
> >     })
> >     Name (_DSD, Package (0x02)  // _DSD: Device-Specific Data
> >     {
> >         ToUUID ("daffd814-6eba-4d8c-8a91-bc9bbf4aa301") /* Device Properties for _DSD */,
> >         Package (0x01)
> >         {
> >             Package (0x02)
> >             {
> >                 "privacy-gpio",
> >                 Package (0x04)
> >                 {
> >                     \_SB.PCI0.XHCI.RHUB.HS07,
> >                     Zero,
> >                     Zero,
> >                     One
> >                 }
> >             }
> >         }
> >     })
> >   }
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_ctrl.c   |   6 ++
> >  drivers/media/usb/uvc/uvc_driver.c | 106 +++++++++++++++++++++++++++++
> >  drivers/media/usb/uvc/uvcvideo.h   |  12 ++++
> >  3 files changed, 124 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index 531816762892..53da1d984883 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -1302,6 +1302,9 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
> >
> >       mutex_unlock(&chain->ctrl_mutex);
> >
> > +     if (!w->urb)
> > +             return;
>
> A small comment to explain why would be useful.
>
> > +
> >       /* Resubmit the URB. */
> >       w->urb->interval = dev->int_ep->desc.bInterval;
> >       ret = usb_submit_urb(w->urb, GFP_KERNEL);
> > @@ -2286,6 +2289,9 @@ int uvc_ctrl_init_device(struct uvc_device *dev)
> >               } else if (UVC_ENTITY_TYPE(entity) == UVC_ITT_CAMERA) {
> >                       bmControls = entity->camera.bmControls;
> >                       bControlSize = entity->camera.bControlSize;
> > +             } else if (UVC_ENTITY_TYPE(entity) == UVC_EXT_GPIO_UNIT) {
> > +                     bmControls = entity->gpio.bmControls;
> > +                     bControlSize = entity->gpio.bControlSize;
> >               }
> >
> >               /* Remove bogus/blacklisted controls */
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index 534629ecd60d..498de09da07e 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -7,6 +7,7 @@
> >   */
> >
> >  #include <linux/atomic.h>
> > +#include <linux/gpio/consumer.h>
> >  #include <linux/kernel.h>
> >  #include <linux/list.h>
> >  #include <linux/module.h>
> > @@ -1020,6 +1021,7 @@ static int uvc_parse_streaming(struct uvc_device *dev,
> >  }
> >
> >  static const u8 uvc_camera_guid[16] = UVC_GUID_UVC_CAMERA;
> > +static const u8 uvc_gpio_guid[16] = UVC_GUID_EXT_GPIO_CONTROLLER;
> >  static const u8 uvc_media_transport_input_guid[16] =
> >       UVC_GUID_UVC_MEDIA_TRANSPORT_INPUT;
> >  static const u8 uvc_processing_guid[16] = UVC_GUID_UVC_PROCESSING;
> > @@ -1053,6 +1055,9 @@ static struct uvc_entity *uvc_alloc_entity(u16 type, u16 id,
> >        * is initialized by the caller.
> >        */
> >       switch (type) {
> > +     case UVC_EXT_GPIO_UNIT:
> > +             memcpy(entity->guid, uvc_gpio_guid, 16);
> > +             break;
> >       case UVC_ITT_CAMERA:
> >               memcpy(entity->guid, uvc_camera_guid, 16);
> >               break;
> > @@ -1466,6 +1471,93 @@ static int uvc_parse_control(struct uvc_device *dev)
> >       return 0;
> >  }
>
> Can we add
>
> /* -----------------------------------------------------------------------------
>  * Privacy GPIO
>  */
>
> here ?
>
> > +static int uvc_gpio_get_cur(struct uvc_device *dev, struct uvc_entity *entity,
> > +                         u8 cs, void *data, u16 size)
> > +{
> > +     if (cs != UVC_CT_PRIVACY_CONTROL || size < 1)
> > +             return -EINVAL;
> > +
> > +     *(uint8_t *)data = gpiod_get_value(entity->gpio.gpio_privacy);
> > +     return 0;
> > +}
> > +
> > +static int uvc_gpio_get_info(struct uvc_device *dev, struct uvc_entity *entity,
> > +                          u8 cs, u8 *caps)
> > +{
> > +     if (cs != UVC_CT_PRIVACY_CONTROL)
> > +             return -EINVAL;
> > +
> > +     *caps = UVC_CONTROL_CAP_GET | UVC_CONTROL_CAP_AUTOUPDATE;
> > +     return 0;
> > +}
> > +
> > +static irqreturn_t uvc_privacy_gpio_irq(int irq, void *data)
> > +{
> > +     struct uvc_device *dev = data;
> > +     struct uvc_video_chain *chain;
> > +     struct uvc_entity *unit;
> > +     u8 value;
> > +
> > +     /* GPIO entities are always on the first chain */
>
>
> s/chain/chain./
>
> > +     chain = list_first_entry(&dev->chains, struct uvc_video_chain, list);
> > +     list_for_each_entry(unit, &dev->entities, list) {
>
> Can we iterate over entities in the chain instead ?
>
> I'd be actually tempted to pass the pointer to the entity as data. We
> would however need to add a chain pointer to uvc_entity. Not sure if
> it's worth it, up to you.
>
> > +             if (UVC_ENTITY_TYPE(unit) != UVC_EXT_GPIO_UNIT)
> > +                     continue;
> > +             value = gpiod_get_value(unit->gpio.gpio_privacy);
>
> Could this sleep ? Should we use a threaded IRQ ?

get_value() should not sleep, but there are platforms that may sleep
to get the irq.

In order to support them I have converted to threaded_irq in the next version
and called gpio_get_value_cansleep()

>
> > +             uvc_ctrl_status_event(NULL, chain, unit->controls, &value);
> > +             return IRQ_HANDLED;
> > +     }
> > +
> > +     return IRQ_HANDLED;
> > +}
> > +
> > +static int uvc_parse_gpio(struct uvc_device *dev)
>
> How about making the naming scheme consistent, by using a uvc_gpio_
> prefix for all four functions ?
>
> > +{
> > +     struct uvc_entity *unit;
> > +     struct gpio_desc *gpio_privacy;
> > +     int irq;
> > +     int ret;
> > +
> > +     gpio_privacy = devm_gpiod_get_optional(&dev->udev->dev, "privacy",
> > +                                            GPIOD_IN);
> > +     if (IS_ERR(gpio_privacy))
> > +             return PTR_ERR(gpio_privacy);
> > +
> > +     if (!gpio_privacy)
> > +             return 0;
>
> This could be folded in
>
>         if (IS_ERR_OR_NULL(gpio_privacy))
>                 return PTR_ERR_OR_ZERO(gpio_privacy);
>
> Up to you.
>
> > +
> > +     unit = uvc_alloc_entity(UVC_EXT_GPIO_UNIT, UVC_EXT_GPIO_UNIT_ID, 0, 1);
> > +     if (!unit)
> > +             return -ENOMEM;
> > +
> > +     unit->gpio.gpio_privacy = gpio_privacy;
> > +     unit->gpio.bControlSize = 1;
> > +     unit->gpio.bmControls = (u8 *)unit + sizeof(*unit);
> > +     unit->gpio.bmControls[0] = 1;
> > +     unit->get_cur = uvc_gpio_get_cur;
> > +     unit->get_info = uvc_gpio_get_info;
> > +
> > +     sprintf(unit->name, "GPIO Unit");
>
> Other unit names don't contain "Unit", should this be just "GPIO" ?
>
> > +
> > +     list_add_tail(&unit->list, &dev->entities);
> > +
> > +     irq = gpiod_to_irq(gpio_privacy);
> > +     if (irq == -EPROBE_DEFER)
> > +             return -EPROBE_DEFER;
>
> Can this happen in practice ?

Yes :(, Eg:
If the irq is handled by an GPIO expansion via I2C, and it has not
been probed yet.

>
> > +
> > +     if (irq < 0)
> > +             return 0;
>
> So this will succeed, with the GPIO unit created, but it won't be
> operational. Is this desired ? Shouldn't we at least print a warning ?

If there is no IRQ, the unit is still functional, but instead of
sending events when the gpio changes, the user will have to poll it.

>
> I also wonder if we should create the GPIO unit in this cases. Wouldn't
> it be more confusing for userspace to see the privacy control being
> exposed, but without it being functional ? Maybe the call to
> gpiod_to_irq should be moved to before uvc_alloc_entity() ?
>
> > +
> > +     ret = devm_request_irq(&dev->udev->dev, irq, uvc_privacy_gpio_irq,
> > +                            IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING,
> > +                            "uvc_privacy_gpio", dev);
> > +     if (ret < 0)
> > +             dev_warn(&dev->udev->dev,
> > +                    "Unable to request uvc_privacy_gpio irq. Continuing\n");
>
> s/uvc_privacy_gpio irq/privacy GPIO IRQ/ ?
>
> There's also a race condition, as soon as the IRQ is requested, it could
> fire, and the driver isn't fully initialized. Walking the chain in the
> IRQ handler while entities are added to the chain could lead to a crash.
> I see two options, either adding a flag to tell that initialization is
> complete and returning from the interrupt handler when the flag isn't
> set, or moving IRQ registration to a separate function, called later
> during the initialization. I think I have a preference for the latter.
>
> > +
> > +     return 0;
> > +}
> > +
> >  /* ------------------------------------------------------------------------
> >   * UVC device scan
> >   */
> > @@ -1917,6 +2009,7 @@ static int uvc_scan_device(struct uvc_device *dev)
> >  {
> >       struct uvc_video_chain *chain;
> >       struct uvc_entity *term;
> > +     struct uvc_entity *unit;
> >
> >       list_for_each_entry(term, &dev->entities, list) {
> >               if (!UVC_ENTITY_IS_OTERM(term))
> > @@ -1955,6 +2048,13 @@ static int uvc_scan_device(struct uvc_device *dev)
> >               return -1;
> >       }
> >
> > +     /* Add GPIO entities to the first chain */
>
> s/chain/chain./
>
> > +     chain = list_first_entry(&dev->chains, struct uvc_video_chain, list);
> > +     list_for_each_entry(unit, &dev->entities, list) {
> > +             if (UVC_ENTITY_TYPE(unit) == UVC_EXT_GPIO_UNIT)
> > +                     list_add_tail(&unit->chain, &chain->entities);
> > +     }
> > +
> >       return 0;
> >  }
> >
> > @@ -2287,6 +2387,12 @@ static int uvc_probe(struct usb_interface *intf,
> >               goto error;
> >       }
> >
> > +     /* Parse the associated GPIOs */
>
> s/GPIOs/GPIOs./
>
> > +     if (uvc_parse_gpio(dev) < 0) {
> > +             uvc_trace(UVC_TRACE_PROBE, "Unable to parse UVC GPIOs\n");
> > +             goto error;
> > +     }
> > +
> >       uvc_printk(KERN_INFO, "Found UVC %u.%02x device %s (%04x:%04x)\n",
> >               dev->uvc_version >> 8, dev->uvc_version & 0xff,
> >               udev->product ? udev->product : "<unnamed>",
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index ae464ba83f4f..f87d14fb3f56 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -6,6 +6,7 @@
> >  #error "The uvcvideo.h header is deprecated, use linux/uvcvideo.h instead."
> >  #endif /* __KERNEL__ */
> >
> > +#include <linux/gpio/consumer.h>
>
> We can use a forward declaration of struct gpio_desc in this file.
>
> >  #include <linux/kernel.h>
> >  #include <linux/poll.h>
> >  #include <linux/usb.h>
> > @@ -37,6 +38,8 @@
> >       (UVC_ENTITY_IS_TERM(entity) && \
> >       ((entity)->type & 0x8000) == UVC_TERM_OUTPUT)
> >
> > +#define UVC_EXT_GPIO_UNIT 0x7ffe
> > +#define UVC_EXT_GPIO_UNIT_ID 0x100
>
> Maybe a couple of tabs to align this with the other defines above ?
>
> >
> >  /* ------------------------------------------------------------------------
> >   * GUIDs
> > @@ -56,6 +59,9 @@
> >  #define UVC_GUID_UVC_SELECTOR \
> >       {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
> >        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02}
> > +#define UVC_GUID_EXT_GPIO_CONTROLLER \
> > +     {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, \
> > +      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x03}
> >
> >  #define UVC_GUID_FORMAT_MJPEG \
> >       { 'M',  'J',  'P',  'G', 0x00, 0x00, 0x10, 0x00, \
> > @@ -348,6 +354,12 @@ struct uvc_entity {
> >                       u8  *bmControls;
> >                       u8  *bmControlsType;
> >               } extension;
> > +
> > +             struct {
> > +                     u8  bControlSize;
> > +                     u8  *bmControls;
> > +                     struct gpio_desc *gpio_privacy;
> > +             } gpio;
> >       };
> >
> >       u8 bNrInPins;
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda

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