Re: [PATCH v4] HID: google: add google hammer HID driver

From: Nicolas Boichat
Date: Wed Mar 14 2018 - 21:22:27 EST

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In reply to: Dmitry Torokhov: "Re: [PATCH v4] HID: google: add google hammer HID driver"
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On Thu, Mar 15, 2018 at 2:05 AM, Dmitry Torokhov <dtor@xxxxxxxxxxxx> wrote:
> On Wed, Mar 14, 2018 at 9:16 AM, Benjamin Tissoires
> <benjamin.tissoires@xxxxxxxxxx> wrote:
>>
>> Hi Nicolas,
>>
>> On Wed, Mar 14, 2018 at 6:22 AM, Nicolas Boichat <drinkcat@xxxxxxxxxxxx> wrote:
>> > From: Wei-Ning Huang <wnhuang@xxxxxxxxxxxx>
>> >
>> > Add Google hammer HID driver. This driver allow us to control hammer
>> > keyboard backlight and support future features.
>> >
>> > We add a new HID quirk, that allows us to have the keyboard interface
>> > to bind to google-hammer driver, while the touchpad interface can
>> > bind to the multitouch driver.
>> >
>> > Signed-off-by: Wei-Ning Huang <wnhuang@xxxxxxxxxx>
>> > Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
>> > ---
>> >
>> > Changes since v3:
>> > - Rebase on latest linux-next/master, which moved the quirk list from
>> > hid-core.c to hid-quirks.c. Also, completely rework the logic to make
>> > it possible to bind google-hammer driver to keyboard interface, and
>> > generic multitouch driver to touchpad interface, as it is much simpler
>> > to do now that quirks are read early in hid_add_device.
>>
>> Ouch, this logic seems too convoluted for me.
>>
>> Just to be sure:
>> - some of your devices export 2 USB interfaces on the same device (so
>> same VID/PID)
>> - one of this interface should be handled by hid-multitouch
>> - the other should be handled by hid-google-hammer
>> - the purpose of the new quirk and HID class are to allow
>> hid-google-hammer to only bind on the non multitouch interface
>>
>> Am I correct?
>>
>> If I am, given that we now don't need to blacklist the drivers for
>> hid-generic since e04a0442d33b8cf183bba38646447b891bb02123, I do not
>> understand why simply declaring "{ HID_DEVICE(BUS_USB,
>> HID_GROUP_GENERIC, USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_HAMMER)
>> }," (same for the 2 others) is not enough to have hid-google-hammer
>> binding only on the non-multitouch interface.
>>
>> Could you please give a shot at it?
>>
>
> Ah, cool, if we now forcibly try to rebind devices from generic HID to
> specialized driver when it appears, then we indeed to not have to do
> this dance with "overrides".

Nice, that works, thanks Benjamin. v5 coming up in a few minutes.

>>
>> > - Add dynamic backlight detection support (only such devices have an
>> > output HID descriptor).
>> > - Add support for wand (one more USB product ID).
>> > - Add SPDX-License-Identifier, fix one minor formatting issue.
>> >
>> > drivers/hid/Kconfig | 6 ++
>> > drivers/hid/Makefile | 1 +
>> > drivers/hid/hid-core.c | 4 ++
>> > drivers/hid/hid-google-hammer.c | 116 ++++++++++++++++++++++++++++++++
>> > drivers/hid/hid-ids.h | 3 +
>> > drivers/hid/hid-quirks.c | 5 ++
>> > include/linux/hid.h | 2 +
>> > 7 files changed, 137 insertions(+)
>> > create mode 100644 drivers/hid/hid-google-hammer.c
>> >
>> > diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
>> > index 1fce4c94e5ac..60252fd796f6 100644
>> > --- a/drivers/hid/Kconfig
>> > +++ b/drivers/hid/Kconfig
>> > @@ -339,6 +339,12 @@ config HOLTEK_FF
>> > Say Y here if you have a Holtek On Line Grip based game controller
>> > and want to have force feedback support for it.
>> >
>> > +config HID_GOOGLE_HAMMER
>> > + tristate "Google Hammer Keyboard"
>> > + depends on USB_HID && LEDS_CLASS
>> > + ---help---
>> > + Say Y here if you have a Google Hammer device.
>> > +
>> > config HID_GT683R
>> > tristate "MSI GT68xR LED support"
>> > depends on LEDS_CLASS && USB_HID
>> > diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
>> > index 713601c7bfa6..17a8bd97da9d 100644
>> > --- a/drivers/hid/Makefile
>> > +++ b/drivers/hid/Makefile
>> > @@ -45,6 +45,7 @@ obj-$(CONFIG_HID_ELO) += hid-elo.o
>> > obj-$(CONFIG_HID_EZKEY) += hid-ezkey.o
>> > obj-$(CONFIG_HID_GEMBIRD) += hid-gembird.o
>> > obj-$(CONFIG_HID_GFRM) += hid-gfrm.o
>> > +obj-$(CONFIG_HID_GOOGLE_HAMMER) += hid-google-hammer.o
>> > obj-$(CONFIG_HID_GT683R) += hid-gt683r.o
>> > obj-$(CONFIG_HID_GYRATION) += hid-gyration.o
>> > obj-$(CONFIG_HID_HOLTEK) += hid-holtek-kbd.o
>> > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
>> > index 36af26c2565b..61c7d135d680 100644
>> > --- a/drivers/hid/hid-core.c
>> > +++ b/drivers/hid/hid-core.c
>> > @@ -2116,6 +2116,10 @@ int hid_add_device(struct hid_device *hdev)
>> > ret = hid_scan_report(hdev);
>> > if (ret)
>> > hid_warn(hdev, "bad device descriptor (%d)\n", ret);
>> > +
>> > + if (hdev->quirks & HID_QUIRK_NO_GENERIC &&
>> > + hdev->group == HID_GROUP_GENERIC)
>> > + hdev->group = HID_GROUP_GENERIC_OVERRIDE;
>> > }
>> >
>> > /* XXX hack, any other cleaner solution after the driver core
>> > diff --git a/drivers/hid/hid-google-hammer.c b/drivers/hid/hid-google-hammer.c
>> > new file mode 100644
>> > index 000000000000..e7ad042a8464
>> > --- /dev/null
>> > +++ b/drivers/hid/hid-google-hammer.c
>> > @@ -0,0 +1,116 @@
>> > +// SPDX-License-Identifier: GPL-2.0+
>> > +/*
>> > + * HID driver for Google Hammer device.
>> > + *
>> > + * Copyright (c) 2017 Google Inc.
>> > + * Author: Wei-Ning Huang <wnhuang@xxxxxxxxxx>
>> > + */
>> > +
>> > +/*
>> > + * This program is free software; you can redistribute it and/or modify it
>> > + * under the terms of the GNU General Public License as published by the Free
>> > + * Software Foundation; either version 2 of the License, or (at your option)
>> > + * any later version.
>> > + */
>> > +
>> > +#include <linux/hid.h>
>> > +#include <linux/leds.h>
>> > +#include <linux/module.h>
>> > +#include <linux/usb.h>
>>
>> Generally that's a no from me to include usb.h. I'd rather have you
>> decide on which interface to create the LEDs based on the report
>> descriptors, so we can replay the device with uhid without crashing
>> the kernel.
>>
>> > +
>> > +#include "hid-ids.h"
>> > +
>> > +#define MAX_BRIGHTNESS 100
>> > +
>> > +struct hammer_kbd_leds {
>> > + struct led_classdev cdev;
>> > + struct hid_device *hdev;
>> > + u8 buf[2] ____cacheline_aligned;
>> > +};
>> > +
>> > +static int hammer_kbd_brightness_set_blocking(struct led_classdev *cdev,
>> > + enum led_brightness br)
>> > +{
>> > + struct hammer_kbd_leds *led = container_of(cdev,
>> > + struct hammer_kbd_leds,
>> > + cdev);
>> > + int ret;
>> > +
>> > + led->buf[0] = 0;
>> > + led->buf[1] = br;
>> > +
>> > + ret = hid_hw_output_report(led->hdev, led->buf, sizeof(led->buf));
>> > + if (ret == -ENOSYS)
>> > + ret = hid_hw_raw_request(led->hdev, 0, led->buf,
>> > + sizeof(led->buf),
>> > + HID_OUTPUT_REPORT,
>> > + HID_REQ_SET_REPORT);
>> > + if (ret < 0)
>> > + hid_err(led->hdev, "failed to set keyboard backlight: %d\n",
>> > + ret);
>> > + return ret;
>> > +}
>> > +
>> > +static int hammer_register_leds(struct hid_device *hdev)
>> > +{
>> > + struct hammer_kbd_leds *kbd_backlight;
>> > +
>> > + kbd_backlight = devm_kzalloc(&hdev->dev,
>> > + sizeof(*kbd_backlight),
>> > + GFP_KERNEL);
>> > + if (!kbd_backlight)
>> > + return -ENOMEM;
>> > +
>> > + kbd_backlight->hdev = hdev;
>> > + kbd_backlight->cdev.name = "hammer::kbd_backlight";
>> > + kbd_backlight->cdev.max_brightness = MAX_BRIGHTNESS;
>> > + kbd_backlight->cdev.brightness_set_blocking =
>> > + hammer_kbd_brightness_set_blocking;
>> > + kbd_backlight->cdev.flags = LED_HW_PLUGGABLE;
>> > +
>> > + /* Set backlight to 0% initially. */
>> > + hammer_kbd_brightness_set_blocking(&kbd_backlight->cdev, 0);
>> > +
>> > + return devm_led_classdev_register(&hdev->dev, &kbd_backlight->cdev);
>> > +}
>> > +
>> > +static int hammer_input_configured(struct hid_device *hdev,
>> > + struct hid_input *hi)
>> > +{
>> > + struct usb_interface *intf = to_usb_interface(hdev->dev.parent);
>> > +
>> > + struct list_head *report_list =
>> > + &hdev->report_enum[HID_OUTPUT_REPORT].report_list;
>> > +
>> > + if (intf->cur_altsetting->desc.bInterfaceProtocol ==
>> > + USB_INTERFACE_PROTOCOL_KEYBOARD && !list_empty(report_list)) {
>>
>> See above. I am pretty sure you can find something in the report
>> descriptor to discriminate the LED capable device from the others.
>>
>> Cheers,
>> Benjamin
>>
>> > + int err = hammer_register_leds(hdev);
>> > +
>> > + if (err)
>> > + hid_warn(hdev,
>> > + "Failed to register keyboard backlight: %d\n",
>> > + err);
>> > + }
>> > +
>> > + return 0;
>> > +}
>> > +
>> > +static const struct hid_device_id hammer_devices[] = {
>> > + { HID_DEVICE(BUS_USB, HID_GROUP_GENERIC_OVERRIDE,
>> > + USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_HAMMER) },
>> > + { HID_DEVICE(BUS_USB, HID_GROUP_GENERIC_OVERRIDE,
>> > + USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_STAFF) },
>> > + { HID_DEVICE(BUS_USB, HID_GROUP_GENERIC_OVERRIDE,
>> > + USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_WAND) },
>> > + { }
>> > +};
>> > +MODULE_DEVICE_TABLE(hid, hammer_devices);
>> > +
>> > +static struct hid_driver hammer_driver = {
>> > + .name = "hammer",
>> > + .id_table = hammer_devices,
>> > + .input_configured = hammer_input_configured,
>> > +};
>> > +module_hid_driver(hammer_driver);
>> > +
>> > +MODULE_LICENSE("GPL");
>> > diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h
>> > index 41f227a841fb..5a3a7ead3012 100644
>> > --- a/drivers/hid/hid-ids.h
>> > +++ b/drivers/hid/hid-ids.h
>> > @@ -448,7 +448,10 @@
>> > #define USB_DEVICE_ID_GOODTOUCH_000f 0x000f
>> >
>> > #define USB_VENDOR_ID_GOOGLE 0x18d1
>> > +#define USB_DEVICE_ID_GOOGLE_HAMMER 0x5022
>> > #define USB_DEVICE_ID_GOOGLE_TOUCH_ROSE 0x5028
>> > +#define USB_DEVICE_ID_GOOGLE_STAFF 0x502b
>> > +#define USB_DEVICE_ID_GOOGLE_WAND 0x502d
>> >
>> > #define USB_VENDOR_ID_GOTOP 0x08f2
>> > #define USB_DEVICE_ID_SUPER_Q2 0x007f
>> > diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
>> > index 587e2681a53f..d112a14da200 100644
>> > --- a/drivers/hid/hid-quirks.c
>> > +++ b/drivers/hid/hid-quirks.c
>> > @@ -84,6 +84,11 @@ static const struct hid_device_id hid_quirks[] = {
>> > { HID_USB_DEVICE(USB_VENDOR_ID_FREESCALE, USB_DEVICE_ID_FREESCALE_MX28), HID_QUIRK_NOGET },
>> > { HID_USB_DEVICE(USB_VENDOR_ID_FUTABA, USB_DEVICE_ID_LED_DISPLAY), HID_QUIRK_NO_INIT_REPORTS },
>> > { HID_USB_DEVICE(USB_VENDOR_ID_GREENASIA, USB_DEVICE_ID_GREENASIA_DUAL_USB_JOYPAD), HID_QUIRK_MULTI_INPUT },
>> > +#if IS_ENABLED(CONFIG_HID_GOOGLE_HAMMER)
>> > + { HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_HAMMER), HID_QUIRK_NO_GENERIC },
>> > + { HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_STAFF), HID_QUIRK_NO_GENERIC },
>> > + { HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_WAND), HID_QUIRK_NO_GENERIC },
>> > +#endif
>> > { HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_DRIVING), HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT },
>> > { HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_FIGHTING), HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT },
>> > { HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_FLYING), HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT },
>> > diff --git a/include/linux/hid.h b/include/linux/hid.h
>> > index dfea5a656a1a..f2655265f8b5 100644
>> > --- a/include/linux/hid.h
>> > +++ b/include/linux/hid.h
>> > @@ -340,6 +340,7 @@ struct hid_item {
>> > #define HID_QUIRK_NO_EMPTY_INPUT 0x00000100
>> > /* 0x00000200 reserved for backward compatibility, was NO_INIT_INPUT_REPORTS */
>> > #define HID_QUIRK_ALWAYS_POLL 0x00000400
>> > +#define HID_QUIRK_NO_GENERIC 0x00000800
>> > #define HID_QUIRK_SKIP_OUTPUT_REPORTS 0x00010000
>> > #define HID_QUIRK_SKIP_OUTPUT_REPORT_ID 0x00020000
>> > #define HID_QUIRK_NO_OUTPUT_REPORTS_ON_INTR_EP 0x00040000
>> > @@ -359,6 +360,7 @@ struct hid_item {
>> > #define HID_GROUP_MULTITOUCH 0x0002
>> > #define HID_GROUP_SENSOR_HUB 0x0003
>> > #define HID_GROUP_MULTITOUCH_WIN_8 0x0004
>> > +#define HID_GROUP_GENERIC_OVERRIDE 0x0005
>> >
>> > /*
>> > * Vendor specific HID device groups
>> > --
>> > 2.16.2.804.g6dcf76e118-goog
>> >
<div class="gmail_extra"> <div class="gmail_quote">On Thu, Mar 15,
2018 at 2:05 AM, Dmitry Torokhov <<a
href="mailto:dtor@xxxxxxxxxxxx";
target="_blank">dtor@xxxxxxxxxxxx</a>> wrote: <blockquote
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">On Wed,
Mar 14, 2018 at 9:16 AM, Benjamin Tissoires 
<<a href="mailto:benjamin.tissoires@xxxxxxxxxx";>benjamin.tissoires@xxxxxxxxxx</a>>
wrote: 
> 
> Hi Nicolas, 
> 
> On Wed, Mar 14, 2018 at 6:22 AM, Nicolas Boichat <<a
href="mailto:drinkcat@xxxxxxxxxxxx";>drinkcat@xxxxxxxxxxxx</a>>
wrote: 
> > From: Wei-Ning Huang <<a
href="mailto:wnhuang@xxxxxxxxxxxx";>wnhuang@xxxxxxxxxxxx</a>> 
> > 
> > Add Google hammer HID driver. This driver allow us to
control hammer 
> > keyboard backlight and support future features. 
> > 
> > We add a new HID quirk, that allows us to have the keyboard
interface 
> > to bind to google-hammer driver, while the touchpad interface can 
> > bind to the multitouch driver. 
> > 
> > Signed-off-by: Wei-Ning Huang <<a
href="mailto:wnhuang@xxxxxxxxxx";>wnhuang@xxxxxxxxxx</a>> 
> > Signed-off-by: Nicolas Boichat <<a
href="mailto:drinkcat@xxxxxxxxxxxx";>drinkcat@xxxxxxxxxxxx</a>> 
> > --- 
> > 
> > Changes since v3: 
> >  - Rebase on latest linux-next/master, which moved the
quirk list from 
> >    hid-core.c to hid-quirks.c. Also, completely
rework the logic to make 
> >    it possible to bind google-hammer driver to
keyboard interface, and 
> >    generic multitouch driver to touchpad
interface, as it is much simpler 
> >    to do now that quirks are read early in
hid_add_device. 
> 
> Ouch, this logic seems too convoluted for me. 
> 
> Just to be sure: 
> - some of your devices export 2 USB interfaces on the same device (so 
> same VID/PID) 
> - one of this interface should be handled by hid-multitouch 
> - the other should be handled by hid-google-hammer 
> - the purpose of the new quirk and HID class are to allow 
> hid-google-hammer to only bind on the non multitouch interface 
> 
> Am I correct? 
> 
> If I am, given that we now don't need to blacklist the drivers for 
> hid-generic since e04a0442d33b8cf183bba38646447b891bb02123,
I do not 
> understand why simply declaring  "{ HID_DEVICE(BUS_USB, 
> HID_GROUP_GENERIC,  USB_VENDOR_ID_GOOGLE,
USB_DEVICE_ID_GOOGLE_HAMMER) 
> }," (same for the 2 others) is not enough to have hid-google-hammer 
> binding only on the non-multitouch interface. 
> 
> Could you please give a shot at it? 
> 
 
</div></div>Ah, cool, if we now forcibly try to rebind devices from
generic HID to 
specialized driver when it appears, then we indeed to not have to do 
this dance with "overrides". 
<div class="HOEnZb"><div class="h5"> 
> 
> >  - Add dynamic backlight detection support (only such
devices have an 
> >    output HID descriptor). 
> >  - Add support for wand (one more USB product ID). 
> >  - Add SPDX-License-Identifier, fix one minor
formatting issue. 
> > 
> >  drivers/hid/Kconfig         
   |   6 ++ 
> >  drivers/hid/Makefile         
  |   1 + 
> >  drivers/hid/hid-core.c       
  |   4 ++ 
> >  drivers/hid/hid-google-hammer.c | 116
++++++++++++++++++++++++++++++++ 
> >  drivers/hid/hid-ids.h       
   |   3 + 
> >  drivers/hid/hid-quirks.c       
|   5 ++ 
> >  include/linux/hid.h         
   |   2 + 
> >  7 files changed, 137 insertions(+) 
> >  create mode 100644 drivers/hid/hid-google-hammer.c 
> > 
> > diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig 
> > index 1fce4c94e5ac..60252fd796f6 100644 
> > --- a/drivers/hid/Kconfig 
> > +++ b/drivers/hid/Kconfig 
> > @@ -339,6 +339,12 @@ config HOLTEK_FF 
> >           Say Y here if you
have a Holtek On Line Grip based game controller 
> >           and want to have
force feedback support for it. 
> > 
> > +config HID_GOOGLE_HAMMER 
> > +       tristate "Google Hammer Keyboard" 
> > +       depends on USB_HID &&
LEDS_CLASS 
> > +       ---help--- 
> > +       Say Y here if you have a Google
Hammer device. 
> > + 
> >  config HID_GT683R 
> >         tristate "MSI GT68xR LED support" 
> >         depends on LEDS_CLASS
&& USB_HID 
> > diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile 
> > index 713601c7bfa6..17a8bd97da9d 100644 
> > --- a/drivers/hid/Makefile 
> > +++ b/drivers/hid/Makefile 
> > @@ -45,6 +45,7 @@ obj-$(CONFIG_HID_ELO)     
   += hid-elo.o 
> >  obj-$(CONFIG_HID_EZKEY)       
        += hid-ezkey.o 
> >  obj-$(CONFIG_HID_GEMBIRD)      +=
hid-gembird.o 
> >  obj-$(CONFIG_HID_GFRM)       
 += hid-gfrm.o 
> > +obj-$(CONFIG_HID_GOOGLE_HAMMER)     
  += hid-google-hammer.o 
> >  obj-$(CONFIG_HID_GT683R)       +=
hid-gt683r.o 
> >  obj-$(CONFIG_HID_GYRATION)     +=
hid-gyration.o 
> >  obj-$(CONFIG_HID_HOLTEK)       +=
hid-holtek-kbd.o 
> > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c 
> > index 36af26c2565b..61c7d135d680 100644 
> > --- a/drivers/hid/hid-core.c 
> > +++ b/drivers/hid/hid-core.c 
> > @@ -2116,6 +2116,10 @@ int hid_add_device(struct hid_device *hdev) 
> >               
 ret = hid_scan_report(hdev); 
> >               
 if (ret) 
> >               
         hid_warn(hdev, "bad device
descriptor (%d)\n", ret); 
> > + 
> > +               if
(hdev->quirks & HID_QUIRK_NO_GENERIC && 
> > +               
               hdev->group
== HID_GROUP_GENERIC) 
> > +               
       hdev->group =
HID_GROUP_GENERIC_OVERRIDE; 
> >         } 
> > 
> >         /* XXX hack, any other
cleaner solution after the driver core 
> > diff --git a/drivers/hid/hid-google-hammer.c
b/drivers/hid/hid-google-hammer.c 
> > new file mode 100644 
> > index 000000000000..e7ad042a8464 
> > --- /dev/null 
> > +++ b/drivers/hid/hid-google-hammer.c 
> > @@ -0,0 +1,116 @@ 
> > +// SPDX-License-Identifier: GPL-2.0+ 
> > +/* 
> > + *  HID driver for Google Hammer device. 
> > + * 
> > + *  Copyright (c) 2017 Google Inc. 
> > + *  Author: Wei-Ning Huang <<a
href="mailto:wnhuang@xxxxxxxxxx";>wnhuang@xxxxxxxxxx</a>> 
> > + */ 
> > + 
> > +/* 
> > + * This program is free software; you can redistribute it
and/or modify it 
> > + * under the terms of the GNU General Public License as
published by the Free 
> > + * Software Foundation; either version 2 of the License, or
(at your option) 
> > + * any later version. 
> > + */ 
> > + 
> > +#include <linux/hid.h> 
> > +#include <linux/leds.h> 
> > +#include <linux/module.h> 
> > +#include <linux/usb.h> 
> 
> Generally that's a no from me to include usb.h. I'd rather have you 
> decide on which interface to create the LEDs based on the report 
> descriptors, so we can replay the device with uhid without crashing 
> the kernel. 
> 
> > + 
> > +#include "hid-ids.h" 
> > + 
> > +#define MAX_BRIGHTNESS 100 
> > + 
> > +struct hammer_kbd_leds { 
> > +       struct led_classdev cdev; 
> > +       struct hid_device *hdev; 
> > +       u8 buf[2] ____cacheline_aligned; 
> > +}; 
> > + 
> > +static int hammer_kbd_brightness_set_blocking(struct
led_classdev *cdev, 
> > +               enum
led_brightness br) 
> > +{ 
> > +       struct hammer_kbd_leds *led =
container_of(cdev, 
> > +               
                   
              struct
hammer_kbd_leds, 
> > +               
                   
              cdev); 
> > +       int ret; 
> > + 
> > +       led->buf[0] = 0; 
> > +       led->buf[1] = br; 
> > + 
> > +       ret =
hid_hw_output_report(led->hdev, led->buf,
sizeof(led->buf)); 
> > +       if (ret == -ENOSYS) 
> > +               ret
= hid_hw_raw_request(led->hdev, 0, led->buf, 
> > +               
                   
    sizeof(led->buf), 
> > +               
                   
    HID_OUTPUT_REPORT, 
> > +               
                   
    HID_REQ_SET_REPORT); 
> > +       if (ret < 0) 
> > +             
 hid_err(led->hdev, "failed to set keyboard backlight:
%d\n", 
> > +               
       ret); 
> > +       return ret; 
> > +} 
> > + 
> > +static int hammer_register_leds(struct hid_device *hdev) 
> > +{ 
> > +       struct hammer_kbd_leds *kbd_backlight; 
> > + 
> > +       kbd_backlight =
devm_kzalloc(&hdev->dev, 
> > +               
                   
sizeof(*kbd_backlight), 
> > +               
                   
GFP_KERNEL); 
> > +       if (!kbd_backlight) 
> > +             
 return -ENOMEM; 
> > + 
> > +       kbd_backlight->hdev = hdev; 
> > +       kbd_backlight-><a
href="http://cdev.name";
data-saferedirecturl="https://www.google.com/url?hl=en&q=http://cdev.name&source=gmail&ust=1521158409163000&usg=AFQjCNEh3tKanACY7TMM3ATXduCC0nKCtQ";
rel="noreferrer" target="_blank">cdev.name</a> =
"hammer::kbd_backlight"; 
> > +     
 kbd_backlight->cdev.max_brightness = MAX_BRIGHTNESS; 
> > +     
 kbd_backlight->cdev.brightness_set_blocking = 
> > +             
 hammer_kbd_brightness_set_blocking; 
> > +       kbd_backlight->cdev.flags =
LED_HW_PLUGGABLE; 
> > + 
> > +       /* Set backlight to 0% initially. */ 
> > +     
 hammer_kbd_brightness_set_blocking(&kbd_backlight->cdev,
0); 
> > + 
> > +       return
devm_led_classdev_register(&hdev->dev,
&kbd_backlight->cdev); 
> > +} 
> > + 
> > +static int hammer_input_configured(struct hid_device *hdev, 
> > +               
                  struct
hid_input *hi) 
> > +{ 
> > +       struct usb_interface *intf =
to_usb_interface(hdev->dev.parent); 
> > + 
> > +       struct list_head *report_list = 
> > +             
 &hdev->report_enum[HID_OUTPUT_REPORT].report_list; 
> > + 
> > +       if
(intf->cur_altsetting->desc.bInterfaceProtocol == 
> > +         
 USB_INTERFACE_PROTOCOL_KEYBOARD &&
!list_empty(report_list)) { 
> 
> See above. I am pretty sure you can find something in the report 
> descriptor to discriminate the LED capable device from the others. 
> 
> Cheers, 
> Benjamin 
> 
> > +               int
err = hammer_register_leds(hdev); 
> > + 
> > +               if (err) 
> > +               
       hid_warn(hdev, 
> > +               
                "Failed to
register keyboard backlight: %d\n", 
> > +               
                err); 
> > +       } 
> > + 
> > +       return 0; 
> > +} 
> > + 
> > +static const struct hid_device_id hammer_devices[] = { 
> > +       { HID_DEVICE(BUS_USB,
HID_GROUP_GENERIC_OVERRIDE, 
> > +               
    USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_HAMMER)
}, 
> > +       { HID_DEVICE(BUS_USB,
HID_GROUP_GENERIC_OVERRIDE, 
> > +               
    USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_STAFF) }, 
> > +       { HID_DEVICE(BUS_USB,
HID_GROUP_GENERIC_OVERRIDE, 
> > +               
    USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_WAND) }, 
> > +       { } 
> > +}; 
> > +MODULE_DEVICE_TABLE(hid, hammer_devices); 
> > + 
> > +static struct hid_driver hammer_driver = { 
> > +       .name = "hammer", 
> > +       .id_table = hammer_devices, 
> > +       .input_configured =
hammer_input_configured, 
> > +}; 
> > +module_hid_driver(hammer_driver); 
> > + 
> > +MODULE_LICENSE("GPL"); 
> > diff --git a/drivers/hid/hid-ids.h b/drivers/hid/hid-ids.h 
> > index 41f227a841fb..5a3a7ead3012 100644 
> > --- a/drivers/hid/hid-ids.h 
> > +++ b/drivers/hid/hid-ids.h 
> > @@ -448,7 +448,10 @@ 
> >  #define USB_DEVICE_ID_GOODTOUCH_000f   0x000f 
> > 
> >  #define USB_VENDOR_ID_GOOGLE     
     0x18d1 
> > +#define USB_DEVICE_ID_GOOGLE_HAMMER    0x5022 
> >  #define USB_DEVICE_ID_GOOGLE_TOUCH_ROSE 
      0x5028 
> > +#define USB_DEVICE_ID_GOOGLE_STAFF     0x502b 
> > +#define USB_DEVICE_ID_GOOGLE_WAND      0x502d 
> > 
> >  #define USB_VENDOR_ID_GOTOP       
    0x08f2 
> >  #define USB_DEVICE_ID_SUPER_Q2     
   0x007f 
> > diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c 
> > index 587e2681a53f..d112a14da200 100644 
> > --- a/drivers/hid/hid-quirks.c 
> > +++ b/drivers/hid/hid-quirks.c 
> > @@ -84,6 +84,11 @@ static const struct hid_device_id
hid_quirks[] = { 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_FREESCALE,
USB_DEVICE_ID_FREESCALE_MX28), HID_QUIRK_NOGET }, 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_FUTABA, USB_DEVICE_ID_LED_DISPLAY),
HID_QUIRK_NO_INIT_REPORTS }, 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_GREENASIA,
USB_DEVICE_ID_GREENASIA_DUAL_USB_JOYPAD), HID_QUIRK_MULTI_INPUT
}, 
> > +#if IS_ENABLED(CONFIG_HID_GOOGLE_HAMMER) 
> > +       {
HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE,
USB_DEVICE_ID_GOOGLE_HAMMER), HID_QUIRK_NO_GENERIC }, 
> > +       {
HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_STAFF),
HID_QUIRK_NO_GENERIC }, 
> > +       {
HID_USB_DEVICE(USB_VENDOR_ID_GOOGLE, USB_DEVICE_ID_GOOGLE_WAND),
HID_QUIRK_NO_GENERIC }, 
> > +#endif 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_DRIVING),
HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT }, 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_FIGHTING),
HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT }, 
> >         {
HID_USB_DEVICE(USB_VENDOR_ID_HAPP, USB_DEVICE_ID_UGCI_FLYING),
HID_QUIRK_BADPAD | HID_QUIRK_MULTI_INPUT }, 
> > diff --git a/include/linux/hid.h b/include/linux/hid.h 
> > index dfea5a656a1a..f2655265f8b5 100644 
> > --- a/include/linux/hid.h 
> > +++ b/include/linux/hid.h 
> > @@ -340,6 +340,7 @@ struct hid_item { 
> >  #define HID_QUIRK_NO_EMPTY_INPUT     
         0x00000100 
> >  /* 0x00000200 reserved for backward compatibility, was
NO_INIT_INPUT_REPORTS */ 
> >  #define HID_QUIRK_ALWAYS_POLL     
            0x00000400 
> > +#define HID_QUIRK_NO_GENERIC       
           0x00000800 
> >  #define HID_QUIRK_SKIP_OUTPUT_REPORTS   
      0x00010000 
> >  #define HID_QUIRK_SKIP_OUTPUT_REPORT_ID 
              0x00020000 
> >  #define HID_QUIRK_NO_OUTPUT_REPORTS_ON_INTR_EP
0x00040000 
> > @@ -359,6 +360,7 @@ struct hid_item { 
> >  #define HID_GROUP_MULTITOUCH     
             0x0002 
> >  #define HID_GROUP_SENSOR_HUB     
             0x0003 
> >  #define HID_GROUP_MULTITOUCH_WIN_8     
       0x0004 
> > +#define HID_GROUP_GENERIC_OVERRIDE     
       0x0005 
> > 
> >  /* 
> >   * Vendor specific HID device groups 
> > -- 
> > 2.16.2.804.g6dcf76e118-goog 
> > 
</div></div></blockquote></div> </div>

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