Consistently Use the same style of variable type in hibmc_drm_de.c.
Signed-off-by: NTian Tao <tiantao6@hisilicon.com>
Acked-by: NThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1602808711-65193-2-git-send-email-tiantao6@hisilicon.com

In function via_mem_alloc`s error branch, DRM_ERROR is protected
in the mutex_lock(&dev->struct_mutex) area.
>From the code, we see that DRM_ERROR is just an error log print
without any struct element, there is no need to protect this.
Signed-off-by: NBernard Zhao <bernard@vivo.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200814083021.8962-1-bernard@vivo.com

platform_get_irq() returns -ERRNO on error.  In such case comparison
to 0 would pass the check.

Fixes: 179c02fe ("drm/tve200: Add new driver for TVE200")
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200827071107.27429-2-krzk@kernel.org

platform_get_irq() returns -ERRNO on error.  In such case comparison
to 0 would pass the check.

Fixes: 5fc537bf ("drm/mcde: Add new driver for ST-Ericsson MCDE")
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200827071107.27429-1-krzk@kernel.org

Add panel timings for YTC700TLAG-05-201C 7" TFT LCD panel from
Yes Optoelectronics Co.,Ltd.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904180821.302194-3-jagan@amarulasolutions.com

Add dt-bindings for YTC700TLAG-05-201C 7" TFT LCD panel from
Yes Optoelectronics Co.,Ltd.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904180821.302194-2-jagan@amarulasolutions.com

Add vendor dt-bindings for Yes Optoelectronics Co.,Ltd.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904180821.302194-1-jagan@amarulasolutions.com

Eliminate the following coccicheck warning:

drivers/video/fbdev/fsl-diu-fb.c:1428:5-8: Unneeded variable: "res".
Return "0" on line 1450
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Acked-by: NGustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910140558.1191423-1-yanaijie@huawei.com

Eliminate the following coccicheck warning:

drivers/video/fbdev/sis/sis_accel.h:143:72-73: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:144:72-73: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:145:72-73: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:273:75-76: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:274:75-76: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:275:73-74: Unneeded semicolon
drivers/video/fbdev/sis/sis_accel.h:276:75-76: Unneeded semicolon
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910140536.1191150-1-yanaijie@huawei.com

This eliminates the following sparse warning:

drivers/gpu/drm/panel/panel-sitronix-st7703.c:156:26: warning: symbol
'jh057n00900_panel_desc' was not declared. Should it be static?
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Reviewed-by: NGuido Günther <agx@sigxcpu.org>
[Use static const]
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200912033809.142773-1-yanaijie@huawei.com

This eliminates the following sparse warning:

drivers/gpu/drm/bridge/adv7511/adv7511_audio.c:58:5: warning: symbol
'adv7511_hdmi_hw_params' was not declared. Should it be static?
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200912033826.142923-1-yanaijie@huawei.com

This eliminates the following sparse warning:

drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c:527:5: warning: symbol
'analogix_dp_start_aux_transaction' was not declared. Should it be
static?
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200912033843.143240-1-yanaijie@huawei.com

Simplify the return expression.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200915032623.1772361-1-liushixin2@huawei.com

Simplify the return expression.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200915032627.1772517-1-liushixin2@huawei.com

Use the devm_platform_ioremap_resource_byname() helper instead of
calling platform_get_resource_byname() and devm_ioremap_resource()
separately.
Signed-off-by: NQilong Zhang <zhangqilong3@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
[fixed warning - unused variable]
[fixed checkpatch warning - fixed indent]
Link: https://patchwork.freedesktop.org/patch/msgid/20200916111353.105914-1-zhangqilong3@huawei.com

Use for_each_child_of_node() macro instead of open coding it.
Signed-off-by: NQinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200916062123.190636-1-miaoqinglang@huawei.com

The ANX7625 is an ultra-low power 4K Mobile HD Transmitter designed
for portable device. It converts MIPI DSI/DPI to DisplayPort 1.3 4K.
Signed-off-by: NXin Ji <xji@analogixsemi.com>
Reported-by: Nkernel test robot <lkp@intel.com>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/528b76c1a4f7b6ea85371bfae4bde389aec4bb24.1600423932.git.xji@analogixsemi.com

anx7625: MIPI to DP transmitter DT schema
Signed-off-by: NXin Ji <xji@analogixsemi.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/bafa02aa50c5c29b3336ca6930c406150a3c60d2.1600423932.git.xji@analogixsemi.com

Simplify the return expression.
Signed-off-by: NQinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921131112.93411-1-miaoqinglang@huawei.com

Simplify the return expression.
Signed-off-by: NQinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921131052.92707-1-miaoqinglang@huawei.com

Simplify the return expression.
Signed-off-by: NQinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org> # dropped gpio-cs5535.c changes
Link: https://patchwork.freedesktop.org/patch/msgid/20200921131051.92661-1-miaoqinglang@huawei.com

Simplify the return expression.
Signed-off-by: NQinglang Miao <miaoqinglang@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921131049.92616-1-miaoqinglang@huawei.com

Simplify the return expression.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921082445.2591825-1-liushixin2@huawei.com

Simplify the return expression.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921082444.2591773-1-liushixin2@huawei.com

Simplify the return expression.
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921082443.2591721-1-liushixin2@huawei.com

Add the support for enabling optional regulator that may be used as VCC
source.
Signed-off-by: NBiju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
[Replaced 'error' variable with 'ret']
[Renamed regulator from 'vcc' to 'power']
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: NBiju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200922105526.5252-1-laurent.pinchart+renesas@ideasonboard.com

Use kobj_to_dev() instead of container_of()
Signed-off-by: NWang Qing <wangqing@vivo.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1600776867-24226-1-git-send-email-wangqing@vivo.com

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/video/fbdev/sis/300vtbl.h:1064:28: warning:
‘SiS300_CHTVVCLKSONTSC’ defined but not used [-Wunused-const-variable=]
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NLi Heng <liheng40@huawei.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1600957106-13741-1-git-send-email-liheng40@huawei.com

Compute new timings to get a framerate of 50fps with a pixel clock
@54Mhz.
Signed-off-by: NYannick Fertre <yannick.fertre@st.com>
Tested-by: NPhilippe Cornu <philippe.cornu@st.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200925141618.12097-1-yannick.fertre@st.com

Because clk_disable_unprepare already checked NULL clock parameter,
so the additional checks are unnecessary, just remove it
Signed-off-by: NXu Wang <vulab@iscas.ac.cn>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200930081859.52431-1-vulab@iscas.ac.cn

On some panels hooked up to the ti-sn65dsi86 bridge chip we found that
link training was failing.  Specifically, we'd see:

  ti_sn65dsi86 2-002d: [drm:ti_sn_bridge_enable] *ERROR* Link training failed, link is off (-5)

The panel was hooked up to a logic analyzer and it was found that, as
part of link training, the bridge chip was writing a 0x1 to DPCD
address 00600h and the panel responded NACK.  As can be seen in header
files, the write of 0x1 to DPCD address 0x600h means we were trying to
write the value DP_SET_POWER_D0 to the register DP_SET_POWER.  The
panel vendor says that a NACK in this case is not unexpected and means
"not ready, try again".

In testing, we found that this panel would respond with a NACK in
about 1/25 times.  Adding the retry logic worked fine and the most
number of tries needed was 3.  Just to be safe, we'll add 10 tries
here and we'll add a little blurb to the logs if we ever need more
than 5.
Signed-off-by: NDouglas Anderson <dianders@chromium.org>
Tested-By: NSteev Klimaszewski <steev@kali.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201002135920.1.I2adbc90b2db127763e2444bd5a4e5bf30e1db8e5@changeid

We need to reset both for the panel to show an image.
Signed-off-by: NGuido Günther <agx@sigxcpu.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/15d3dc7eb4e031f380be1298ed3ac9085626f26b.1602584953.git.agx@sigxcpu.org

The mantix panel needs two reset lines (RESX and TP_RSTN) deasserted to
output an image. Only deasserting RESX is not enough and the display
will stay blank. Deassert in prepare() and assert in unprepare() to keep
device held in reset when off.
Signed-off-by: NGuido Günther <agx@sigxcpu.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/ba71a8ab010d263a8058dd4f711e3bcd95877bf2.1602584953.git.agx@sigxcpu.org

Don't dereference mode which was just NULL checked.
Signed-off-by: NGuido Günther <agx@sigxcpu.org>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/659158549f3c6cc1c71ceed0943e760e861c1206.1602584953.git.agx@sigxcpu.org

video: fbdev: sh_mobile_lcdcfb: Remove redundant null check before clk_prepare_enable/clk_disable_unprepare

Because clk_prepare_enable() and clk_disable_unprepare() already checked
NULL clock parameter, so the additional checks are unnecessary, just
remove them.
Signed-off-by: NXu Wang <vulab@iscas.ac.cn>
Signed-off-by: NThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201014085722.26069-1-vulab@iscas.ac.cn

Because clk_prepare_enable() and clk_disable_unprepare() already checked
NULL clock parameter, so the additional checks are unnecessary, just
remove them.
Signed-off-by: NXu Wang <vulab@iscas.ac.cn>
Signed-off-by: NThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201014084920.25813-1-vulab@iscas.ac.cn

Inspired by a patch by Chris Wilson for vgem. Plus this gives us vmap
at the gem bo level, which we need for generic fbdev emulation.

Luckily shmem also tracks ->vaddr, so we just need to adjust the code
all over a bit to make this fit.

Also wire up handle_to_fd, dunno why that was missing.

v2:
- Drop now unused container_of #define (Melissa)
- Make sure we keep creating cached objects, this is for testing
  (Thomas)
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Melissa Wen <melissa.srw@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Acked-by: NThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: NMelissa Wen <melissa.srw@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201013111027.375999-1-daniel.vetter@ffwll.ch

The only thing we support is xrgb8888.
Acked-by: NThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: NMelissa Wen <melissa.srw@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Melissa Wen <melissa.srw@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201009232156.3916879-1-daniel.vetter@ffwll.ch

The dma-buf API have been used under the assumption that the sg lists
returned from dma_buf_map_attachment() are fully page aligned. Lots of
stuff can break otherwise all over the place. Clarify this in the
documentation and add a check when DMA API debug is enabled.
Signed-off-by: NJianxin Xiong <jianxin.xiong@intel.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1602692161-107096-1-git-send-email-jianxin.xiong@intel.com

I observed this when unplugging a DP monitor whilst a computer is asleep
and then waking it up. This left DP chardev nodes still being present on
the filesystem and accessing these device nodes caused an oops because
drm_dp_aux_dev_get_by_minor() assumes a device exists if it is opened.
This can also be reproduced by creating a device node with mknod(1) and
issuing an open(2)

[166164.933198] BUG: kernel NULL pointer dereference, address: 0000000000000018
[166164.933202] #PF: supervisor read access in kernel mode
[166164.933204] #PF: error_code(0x0000) - not-present page
[166164.933205] PGD 0 P4D 0
[166164.933208] Oops: 0000 [#1] PREEMPT SMP NOPTI
[166164.933211] CPU: 4 PID: 99071 Comm: fwupd Tainted: G        W
5.8.0-rc6+ #1
[166164.933213] Hardware name: LENOVO 20RD002VUS/20RD002VUS, BIOS R16ET25W
(1.11 ) 04/21/2020
[166164.933232] RIP: 0010:drm_dp_aux_dev_get_by_minor+0x29/0x70
[drm_kms_helper]
[166164.933234] Code: 00 0f 1f 44 00 00 55 48 89 e5 41 54 41 89 fc 48 c7
c7 60 01 a4 c0 e8 26 ab 30 d7 44 89 e6 48 c7 c7 80 01 a4 c0 e8 47 94 d6 d6
<8b> 50 18 49 89 c4 48 8d 78 18 85 d2 74 33 8d 4a 01 89 d0 f0 0f b1
[166164.933236] RSP: 0018:ffffb7d7c41cbbf0 EFLAGS: 00010246
[166164.933237] RAX: 0000000000000000 RBX: ffff8a90001fe900 RCX: 0000000000000000
[166164.933238] RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffffffffc0a40180
[166164.933239] RBP: ffffb7d7c41cbbf8 R08: 0000000000000000 R09: ffff8a93e157d6d0
[166164.933240] R10: 0000000000000000 R11: ffffffffc0a40188 R12: 0000000000000003
[166164.933241] R13: ffff8a9402200e80 R14: ffff8a90001fe900 R15: 0000000000000000
[166164.933244] FS:  00007f7fb041eb00(0000) GS:ffff8a9411500000(0000)
knlGS:0000000000000000
[166164.933245] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[166164.933246] CR2: 0000000000000018 CR3: 00000000352c2003 CR4: 00000000003606e0
[166164.933247] Call Trace:
[166164.933264]  auxdev_open+0x1b/0x40 [drm_kms_helper]
[166164.933278]  chrdev_open+0xa7/0x1c0
[166164.933282]  ? cdev_put.part.0+0x20/0x20
[166164.933287]  do_dentry_open+0x161/0x3c0
[166164.933291]  vfs_open+0x2d/0x30
[166164.933297]  path_openat+0xb27/0x10e0
[166164.933306]  ? atime_needs_update+0x73/0xd0
[166164.933309]  do_filp_open+0x91/0x100
[166164.933313]  ? __alloc_fd+0xb2/0x150
[166164.933316]  do_sys_openat2+0x210/0x2d0
[166164.933318]  do_sys_open+0x46/0x80
[166164.933320]  __x64_sys_openat+0x20/0x30
[166164.933328]  do_syscall_64+0x52/0xc0
[166164.933336]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

(gdb) disassemble drm_dp_aux_dev_get_by_minor+0x29
Dump of assembler code for function drm_dp_aux_dev_get_by_minor:
   0x0000000000017b10 <+0>:     callq  0x17b15 <drm_dp_aux_dev_get_by_minor+5>
   0x0000000000017b15 <+5>:     push   %rbp
   0x0000000000017b16 <+6>:     mov    %rsp,%rbp
   0x0000000000017b19 <+9>:     push   %r12
   0x0000000000017b1b <+11>:    mov    %edi,%r12d
   0x0000000000017b1e <+14>:    mov    $0x0,%rdi
   0x0000000000017b25 <+21>:    callq  0x17b2a <drm_dp_aux_dev_get_by_minor+26>
   0x0000000000017b2a <+26>:    mov    %r12d,%esi
   0x0000000000017b2d <+29>:    mov    $0x0,%rdi
   0x0000000000017b34 <+36>:    callq  0x17b39 <drm_dp_aux_dev_get_by_minor+41>
   0x0000000000017b39 <+41>:    mov    0x18(%rax),%edx <=========
   0x0000000000017b3c <+44>:    mov    %rax,%r12
   0x0000000000017b3f <+47>:    lea    0x18(%rax),%rdi
   0x0000000000017b43 <+51>:    test   %edx,%edx
   0x0000000000017b45 <+53>:    je     0x17b7a <drm_dp_aux_dev_get_by_minor+106>
   0x0000000000017b47 <+55>:    lea    0x1(%rdx),%ecx
   0x0000000000017b4a <+58>:    mov    %edx,%eax
   0x0000000000017b4c <+60>:    lock cmpxchg %ecx,(%rdi)
   0x0000000000017b50 <+64>:    jne    0x17b76 <drm_dp_aux_dev_get_by_minor+102>
   0x0000000000017b52 <+66>:    test   %edx,%edx
   0x0000000000017b54 <+68>:    js     0x17b6d <drm_dp_aux_dev_get_by_minor+93>
   0x0000000000017b56 <+70>:    test   %ecx,%ecx
   0x0000000000017b58 <+72>:    js     0x17b6d <drm_dp_aux_dev_get_by_minor+93>
   0x0000000000017b5a <+74>:    mov    $0x0,%rdi
   0x0000000000017b61 <+81>:    callq  0x17b66 <drm_dp_aux_dev_get_by_minor+86>
   0x0000000000017b66 <+86>:    mov    %r12,%rax
   0x0000000000017b69 <+89>:    pop    %r12
   0x0000000000017b6b <+91>:    pop    %rbp
   0x0000000000017b6c <+92>:    retq
   0x0000000000017b6d <+93>:    xor    %esi,%esi
   0x0000000000017b6f <+95>:    callq  0x17b74 <drm_dp_aux_dev_get_by_minor+100>
   0x0000000000017b74 <+100>:   jmp    0x17b5a <drm_dp_aux_dev_get_by_minor+74>
   0x0000000000017b76 <+102>:   mov    %eax,%edx
   0x0000000000017b78 <+104>:   jmp    0x17b43 <drm_dp_aux_dev_get_by_minor+51>
   0x0000000000017b7a <+106>:   xor    %r12d,%r12d
   0x0000000000017b7d <+109>:   jmp    0x17b5a <drm_dp_aux_dev_get_by_minor+74>
End of assembler dump.

(gdb) list *drm_dp_aux_dev_get_by_minor+0x29
0x17b39 is in drm_dp_aux_dev_get_by_minor (drivers/gpu/drm/drm_dp_aux_dev.c:65).
60      static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
61      {
62              struct drm_dp_aux_dev *aux_dev = NULL;
63
64              mutex_lock(&aux_idr_mutex);
65              aux_dev = idr_find(&aux_idr, index);
66              if (!kref_get_unless_zero(&aux_dev->refcount))
67                      aux_dev = NULL;
68              mutex_unlock(&aux_idr_mutex);
69
(gdb) p/x &((struct drm_dp_aux_dev *)(0x0))->refcount
$8 = 0x18

Looking at the caller, checks on the minor are pushed down to
drm_dp_aux_dev_get_by_minor()

static int auxdev_open(struct inode *inode, struct file *file)
{
    unsigned int minor = iminor(inode);
    struct drm_dp_aux_dev *aux_dev;

    aux_dev = drm_dp_aux_dev_get_by_minor(minor); <====
    if (!aux_dev)
        return -ENODEV;

    file->private_data = aux_dev;
    return 0;
}

Fixes: e94cb37b ("drm/dp: Add a drm_aux-dev module for reading/writing dpcd registers.")
Cc: <stable@vger.kernel.org> # v4.6+
Signed-off-by: NZwane Mwaikambo <zwane@yosper.io>
Reviewed-by: NLyude Paul <lyude@redhat.com>
[added Cc to stable]
Signed-off-by: NLyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/alpine.DEB.2.21.2010122231070.38717@montezuma.home