On trogdor devices I see the following lockdep splat when stopping
youtube with lockdep enabled in the kernel.

 ======================================================
 WARNING: possible circular locking dependency detected
 5.13.0-rc2 #71 Not tainted
 ------------------------------------------------------
 ThreadPoolSingl/3969 is trying to acquire lock:
 ffffff80d4d5c080 (&inst->lock#3){+.+.}-{3:3}, at: vdec_buf_cleanup+0x3c/0x17c [venus_dec]

 but task is already holding lock:
 ffffff80d3c3c4f8 (&q->mmap_lock){+.+.}-{3:3}, at: vb2_core_reqbufs+0xe4/0x390 [videobuf2_common]

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #5 (&q->mmap_lock){+.+.}-{3:3}:
        __mutex_lock_common+0xcc/0xb88
        mutex_lock_nested+0x5c/0x68
        vb2_mmap+0xf4/0x290 [videobuf2_common]
        v4l2_m2m_fop_mmap+0x44/0x50 [v4l2_mem2mem]
        v4l2_mmap+0x5c/0xa4
        mmap_region+0x310/0x5a4
        do_mmap+0x348/0x43c
        vm_mmap_pgoff+0xfc/0x178
        ksys_mmap_pgoff+0x84/0xfc
        __arm64_compat_sys_aarch32_mmap2+0x2c/0x38
        invoke_syscall+0x54/0x110
        el0_svc_common+0x88/0xf0
        do_el0_svc_compat+0x28/0x34
        el0_svc_compat+0x24/0x34
        el0_sync_compat_handler+0xc0/0xf0
        el0_sync_compat+0x19c/0x1c0

 -> #4 (&mm->mmap_lock){++++}-{3:3}:
        __might_fault+0x60/0x88
        filldir64+0x124/0x3a0
        dcache_readdir+0x7c/0x1ec
        iterate_dir+0xc4/0x184
        __arm64_sys_getdents64+0x78/0x170
        invoke_syscall+0x54/0x110
        el0_svc_common+0xa8/0xf0
        do_el0_svc_compat+0x28/0x34
        el0_svc_compat+0x24/0x34
        el0_sync_compat_handler+0xc0/0xf0
        el0_sync_compat+0x19c/0x1c0

 -> #3 (&sb->s_type->i_mutex_key#3){++++}-{3:3}:
        down_write+0x94/0x1f4
        start_creating+0xb0/0x174
        debugfs_create_dir+0x28/0x138
        opp_debug_register+0x88/0xc0
        _add_opp_dev+0x84/0x9c
        _add_opp_table_indexed+0x16c/0x310
        _of_add_table_indexed+0x70/0xb5c
        dev_pm_opp_of_add_table_indexed+0x20/0x2c
        of_genpd_add_provider_onecell+0xc4/0x1c8
        rpmhpd_probe+0x21c/0x278
        platform_probe+0xb4/0xd4
        really_probe+0x140/0x35c
        driver_probe_device+0x90/0xcc
        __device_attach_driver+0xa4/0xc0
        bus_for_each_drv+0x8c/0xd8
        __device_attach+0xc4/0x150
        device_initial_probe+0x20/0x2c
        bus_probe_device+0x40/0xa4
        device_add+0x22c/0x3fc
        of_device_add+0x44/0x54
        of_platform_device_create_pdata+0xb0/0xf4
        of_platform_bus_create+0x1d0/0x350
        of_platform_populate+0x80/0xd4
        devm_of_platform_populate+0x64/0xb0
        rpmh_rsc_probe+0x378/0x3dc
        platform_probe+0xb4/0xd4
        really_probe+0x140/0x35c
        driver_probe_device+0x90/0xcc
        __device_attach_driver+0xa4/0xc0
        bus_for_each_drv+0x8c/0xd8
        __device_attach+0xc4/0x150
        device_initial_probe+0x20/0x2c
        bus_probe_device+0x40/0xa4
        device_add+0x22c/0x3fc
        of_device_add+0x44/0x54
        of_platform_device_create_pdata+0xb0/0xf4
        of_platform_bus_create+0x1d0/0x350
        of_platform_bus_create+0x21c/0x350
        of_platform_populate+0x80/0xd4
        of_platform_default_populate_init+0xb8/0xd4
        do_one_initcall+0x1b4/0x400
        do_initcall_level+0xa8/0xc8
        do_initcalls+0x5c/0x9c
        do_basic_setup+0x2c/0x38
        kernel_init_freeable+0x1a4/0x1ec
        kernel_init+0x20/0x118
        ret_from_fork+0x10/0x30

 -> #2 (gpd_list_lock){+.+.}-{3:3}:
        __mutex_lock_common+0xcc/0xb88
        mutex_lock_nested+0x5c/0x68
        __genpd_dev_pm_attach+0x70/0x18c
        genpd_dev_pm_attach_by_id+0xe4/0x158
        genpd_dev_pm_attach_by_name+0x48/0x60
        dev_pm_domain_attach_by_name+0x2c/0x38
        dev_pm_opp_attach_genpd+0xac/0x160
        vcodec_domains_get+0x94/0x14c [venus_core]
        core_get_v4+0x150/0x188 [venus_core]
        venus_probe+0x138/0x444 [venus_core]
        platform_probe+0xb4/0xd4
        really_probe+0x140/0x35c
        driver_probe_device+0x90/0xcc
        device_driver_attach+0x58/0x7c
        __driver_attach+0xc8/0xe0
        bus_for_each_dev+0x88/0xd4
        driver_attach+0x30/0x3c
        bus_add_driver+0x10c/0x1e0
        driver_register+0x70/0x108
        __platform_driver_register+0x30/0x3c
        0xffffffde113e1044
        do_one_initcall+0x1b4/0x400
        do_init_module+0x64/0x1fc
        load_module+0x17f4/0x1958
        __arm64_sys_finit_module+0xb4/0xf0
        invoke_syscall+0x54/0x110
        el0_svc_common+0x88/0xf0
        do_el0_svc_compat+0x28/0x34
        el0_svc_compat+0x24/0x34
        el0_sync_compat_handler+0xc0/0xf0
        el0_sync_compat+0x19c/0x1c0

 -> #1 (&opp_table->genpd_virt_dev_lock){+.+.}-{3:3}:
        __mutex_lock_common+0xcc/0xb88
        mutex_lock_nested+0x5c/0x68
        _set_required_opps+0x74/0x120
        _set_opp+0x94/0x37c
        dev_pm_opp_set_rate+0xa0/0x194
        core_clks_set_rate+0x28/0x58 [venus_core]
        load_scale_v4+0x228/0x2b4 [venus_core]
        session_process_buf+0x160/0x198 [venus_core]
        venus_helper_vb2_buf_queue+0xcc/0x130 [venus_core]
        vdec_vb2_buf_queue+0xc4/0x140 [venus_dec]
        __enqueue_in_driver+0x164/0x188 [videobuf2_common]
        vb2_core_qbuf+0x13c/0x47c [videobuf2_common]
        vb2_qbuf+0x88/0xec [videobuf2_v4l2]
        v4l2_m2m_qbuf+0x84/0x15c [v4l2_mem2mem]
        v4l2_m2m_ioctl_qbuf+0x24/0x30 [v4l2_mem2mem]
        v4l_qbuf+0x54/0x68
        __video_do_ioctl+0x2bc/0x3bc
        video_usercopy+0x558/0xb04
        video_ioctl2+0x24/0x30
        v4l2_ioctl+0x58/0x68
        v4l2_compat_ioctl32+0x84/0xa0
        __arm64_compat_sys_ioctl+0x12c/0x140
        invoke_syscall+0x54/0x110
        el0_svc_common+0x88/0xf0
        do_el0_svc_compat+0x28/0x34
        el0_svc_compat+0x24/0x34
        el0_sync_compat_handler+0xc0/0xf0
        el0_sync_compat+0x19c/0x1c0

 -> #0 (&inst->lock#3){+.+.}-{3:3}:
        __lock_acquire+0x248c/0x2d6c
        lock_acquire+0x240/0x314
        __mutex_lock_common+0xcc/0xb88
        mutex_lock_nested+0x5c/0x68
        vdec_buf_cleanup+0x3c/0x17c [venus_dec]
        __vb2_queue_free+0x98/0x204 [videobuf2_common]
        vb2_core_reqbufs+0x14c/0x390 [videobuf2_common]
        vb2_reqbufs+0x58/0x74 [videobuf2_v4l2]
        v4l2_m2m_reqbufs+0x58/0x90 [v4l2_mem2mem]
        v4l2_m2m_ioctl_reqbufs+0x24/0x30 [v4l2_mem2mem]
        v4l_reqbufs+0x58/0x6c
        __video_do_ioctl+0x2bc/0x3bc
        video_usercopy+0x558/0xb04
        video_ioctl2+0x24/0x30
        v4l2_ioctl+0x58/0x68
        v4l2_compat_ioctl32+0x84/0xa0
        __arm64_compat_sys_ioctl+0x12c/0x140
        invoke_syscall+0x54/0x110
        el0_svc_common+0x88/0xf0
        do_el0_svc_compat+0x28/0x34
        el0_svc_compat+0x24/0x34
        el0_sync_compat_handler+0xc0/0xf0
        el0_sync_compat+0x19c/0x1c0

 other info that might help us debug this:

 Chain exists of:
   &inst->lock#3 --> &mm->mmap_lock --> &q->mmap_lock

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&q->mmap_lock);
                                lock(&mm->mmap_lock);
                                lock(&q->mmap_lock);
   lock(&inst->lock#3);

  *** DEADLOCK ***

 1 lock held by ThreadPoolSingl/3969:
  #0: ffffff80d3c3c4f8 (&q->mmap_lock){+.+.}-{3:3}, at: vb2_core_reqbufs+0xe4/0x390 [videobuf2_common]

 stack backtrace:
 CPU: 2 PID: 3969 Comm: ThreadPoolSingl Not tainted 5.13.0-rc2 #71
 Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
 Call trace:
  dump_backtrace+0x0/0x1b4
  show_stack+0x24/0x30
  dump_stack+0xe0/0x15c
  print_circular_bug+0x32c/0x388
  check_noncircular+0x138/0x140
  __lock_acquire+0x248c/0x2d6c
  lock_acquire+0x240/0x314
  __mutex_lock_common+0xcc/0xb88
  mutex_lock_nested+0x5c/0x68
  vdec_buf_cleanup+0x3c/0x17c [venus_dec]
  __vb2_queue_free+0x98/0x204 [videobuf2_common]
  vb2_core_reqbufs+0x14c/0x390 [videobuf2_common]
  vb2_reqbufs+0x58/0x74 [videobuf2_v4l2]
  v4l2_m2m_reqbufs+0x58/0x90 [v4l2_mem2mem]
  v4l2_m2m_ioctl_reqbufs+0x24/0x30 [v4l2_mem2mem]
  v4l_reqbufs+0x58/0x6c
  __video_do_ioctl+0x2bc/0x3bc
  video_usercopy+0x558/0xb04
  video_ioctl2+0x24/0x30
  v4l2_ioctl+0x58/0x68
  v4l2_compat_ioctl32+0x84/0xa0
  __arm64_compat_sys_ioctl+0x12c/0x140
  invoke_syscall+0x54/0x110
  el0_svc_common+0x88/0xf0
  do_el0_svc_compat+0x28/0x34
  el0_svc_compat+0x24/0x34
  el0_sync_compat_handler+0xc0/0xf0
  el0_sync_compat+0x19c/0x1c0

The 'gpd_list_lock' is nominally named as such to protect the 'gpd_list'
from concurrent access and mutation. Unfortunately, holding that mutex
around various OPP framework calls leads to lockdep splats because now
we're doing various operations in OPP core such as registering with
debugfs while holding the list lock. We don't need to hold any list
mutex while we're calling into OPP, so let's shrink the locking area of
the 'gpd_list_lock' so that lockdep isn't triggered. This also helps
reduce contention on this lock, which probably doesn't matter much but
at least is nice to have.

Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <linux-pm@vger.kernel.org>
Cc: Viresh Kumar <vireshk@kernel.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>