Re: [PATCH v2] media: v4l2-subdev: Document and enforce .s_stream() requirements

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	Hi Laurent,

On Mon, 18 Sep 2023, Laurent Pinchart wrote:
The subdev .s_stream() operation must not be called to start an already
started subdev, or stop an already stopped one. This requirement has
never been formally documented. Fix it, and catch possible offenders
with a WARN_ON() in the call_s_stream() wrapper.

Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
Changes since v1:

- Add WARN_ON() in call_s_stream()
- Fix typo and language in documentation

Thanks for your patch, which is now commit 009905ec50433259 ("media:
v4l2-subdev: Document and enforce .s_stream() requirements")
in linux-next/master media/master.

This patch causes the below warning during s2idle/s2ram on Salvator-XS
(R-Car H3 ES2.0) and White-Hawk (R-Car V4H).  Koelsch (R-Car M2-W) is not
affected, as its DU does not use the VSP.

    Filesystems sync: 0.014 seconds
    Freezing user space processes
    Freezing user space processes completed (elapsed 0.006 seconds)
    OOM killer disabled.
    Freezing remaining freezable tasks
    Freezing remaining freezable tasks completed (elapsed 0.002 seconds)
    ------------[ cut here ]------------
    WARNING: CPU: 2 PID: 962 at drivers/media/v4l2-core/v4l2-subdev.c:371 call_s_stream+0xd4/0xf0
    CPU: 2 PID: 962 Comm: s2idle Not tainted 6.6.0-rc3-arm64-renesas-00068-g009905ec5043 #2302
    Hardware name: Renesas Salvator-X 2nd version board based on r8a77951 (DT)
    pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
    pc : call_s_stream+0xd4/0xf0
    lr : vsp1_pipeline_stop+0x10c/0x2a4
    sp : ffff800083f635f0
    x29: ffff800083f635f0 x28: 0000000000000000 x27: 0000000000000001
    x26: 0000000000000000 x25: ffff0004c3375b08 x24: ffff0004c3375880
    x23: 0000000000000288 x22: ffff0004c3375b30 x21: 0000000000000000
    x20: ffff0004c3370880 x19: ffff0004c33750f0 x18: 0000000000000001
    x17: 000000040044ffff x16: 00000034b5503510 x15: 0000000000000028
    x14: 0000000000000000 x13: 0000000000000003 x12: 0000000000000000
    x11: 0000000000000000 x10: ffff800082063b78 x9 : ffff800081a5abb8
    x8 : 00000000e50359b8 x7 : 00000000000000ac x6 : 0000000000002b10
    x5 : 0000000000000000 x4 : ffff8000838f8000 x3 : ffff800080932760
    x2 : ffff80008096671c x1 : 0000000000000000 x0 : 0000000000000001
    Call trace:
     call_s_stream+0xd4/0xf0
     vsp1_pipeline_stop+0x10c/0x2a4
     vsp1_du_setup_lif+0x324/0x468
     rcar_du_vsp_disable+0x1c/0x24
     rcar_du_crtc_atomic_disable+0x2f8/0x438
     disable_outputs+0x22c/0x338
     drm_atomic_helper_commit_modeset_disables+0x18/0x44
     rcar_du_atomic_commit_tail+0x90/0xd8
     commit_tail+0x9c/0x178
     drm_atomic_helper_commit+0x18c/0x1a0
     drm_atomic_commit+0xa4/0xd8
     drm_atomic_helper_disable_all+0x1ec/0x200
     drm_atomic_helper_suspend+0xa0/0x208
     drm_mode_config_helper_suspend+0x2c/0x70
     rcar_du_pm_suspend+0x14/0x1c
     platform_pm_suspend+0x28/0x64
     dpm_run_callback+0x34/0x90
     __device_suspend+0x10c/0x3c4
     dpm_suspend+0x140/0x250
     dpm_suspend_start+0x78/0x90
     suspend_devices_and_enter+0x124/0x570
     pm_suspend+0x1ec/0x310
     state_store+0x88/0x124
     kobj_attr_store+0x14/0x24
     sysfs_kf_write+0x48/0x6c
     kernfs_fop_write_iter+0x118/0x1a8
     vfs_write+0x208/0x30c
     ksys_write+0x64/0xec
     __arm64_sys_write+0x18/0x20
     invoke_syscall+0x44/0x108
     el0_svc_common.constprop.0+0x3c/0xdc
     do_el0_svc+0x1c/0x24
     el0_svc+0x40/0xd4
     el0t_64_sync_handler+0x134/0x150
     el0t_64_sync+0x14c/0x150
    irq event stamp: 19852
    hardirqs last  enabled at (19851): [<ffff800080dc3234>] _raw_spin_unlock_irqrestore+0x6c/0x70
    hardirqs last disabled at (19852): [<ffff800080db3f9c>] el1_dbg+0x20/0x80
    softirqs last  enabled at (17806): [<ffff800080010618>] __do_softirq+0x430/0x4e0
    softirqs last disabled at (17799): [<ffff8000800151e0>] ____do_softirq+0xc/0x14
    ---[ end trace 0000000000000000 ]---

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds



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