Re: [PATCH v2 5/6] drm/fb-helper: Schedule deferred-I/O worker after writing to framebuffer

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Hi

Am 23.11.22 um 09:28 schrieb Biju Das:
Hi All,

The below patch in Linux-next 20221123 is causing regression on Renesas {RZ/G2M, R-Car Gen-3}
Platforms.

Steps to reproduce:

Use the arm64 defconfig to build the kernel and then boot the board.

Is there any patch to fix the problem? I am happy to test.

A revert is already on the way. It should reach linux-next by next week.

Best regards
Thomas


Logs:-

[   23.762999] Console: switching to colour frame buffer device 240x67
[   23.763128] ------------[ cut here ]------------
[   23.763133] WARNING: CPU: 3 PID: 278 at drivers/video/fbdev/core/fb_defio.c:340 fb_deferred_io_schedule_flush+0x38/0x40
[   23.763164] Modules linked in: cfg80211(+) rcar_du_drm(+) rcar_mipi_dsi rcar_cmm rcar_lvds snd_soc_hdmi_codec vsp1 dw_hdmi_cec dw_hdmi_i2s_audio rcar_fdp1 v4l2_mem2mem videobuf2_vmalloc rcar_dw_hdmi videobuf2_dma_contig dw_hdmi videobuf2_memops hci_uart videobuf2_v4l2 cec videobuf2_common crct10dif_ce btqca drm_display_helper snd_soc_audio_graph_card drm_dma_helper videodev snd_soc_simple_card_utils btbcm wlcore_sdio mc rcar_fcp display_connector bluetooth rcar_can drm_kms_helper ecdh_generic renesas_usb3 ecc snd_soc_rcar drm rfkill can_dev pwm_rcar usb_dmac renesas_usbhs phy_rcar_gen3_usb3 ipv6
[   23.763314] CPU: 3 PID: 278 Comm: systemd-udevd Not tainted 6.1.0-rc6-next-20221123-10432-g736b6d81d93c #314
[   23.763323] Hardware name: HopeRun HiHope RZ/G2M with sub board (DT)
[   23.763329] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   23.763337] pc : fb_deferred_io_schedule_flush+0x38/0x40
[   23.763344] lr : drm_fb_helper_sys_imageblit+0xa8/0xc4 [drm_kms_helper]
[   23.763474] sp : ffff80000ac5b3c0
[   23.763478] x29: ffff80000ac5b3c0 x28: 00000000ffffffff x27: 0000000000000010
[   23.763489] x26: ffff0005c1356000 x25: ffff0005c3a80800 x24: ffff0005c02528cc
[   23.763499] x23: 0000000000000000 x22: 0000000000000180 x21: 0000000000000008
[   23.763509] x20: 0000000000000010 x19: ffff0005c0252800 x18: 0000000000000001
[   23.763519] x17: 0000000000000004 x16: 0000000000000000 x15: 0000000000000000
[   23.763529] x14: 0000000000000020 x13: 0000000000000000 x12: 0000000000000020
[   23.763539] x11: 00000000ffffffff x10: 0000000000000001 x9 : 0000000000000001
[   23.763549] x8 : ffff0005c1356010 x7 : 0000000000000008 x6 : 0000000000000000
[   23.763559] x5 : 0000000000000190 x4 : 0000000000000180 x3 : 0000000000000008
[   23.763569] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff0005c3a80800
[   23.763580] Call trace:
[   23.763585]  fb_deferred_io_schedule_flush+0x38/0x40
[   23.763594]  drm_fbdev_fb_imageblit+0x38/0x70 [drm_kms_helper]
[   23.763671]  soft_cursor+0x15c/0x200
[   23.763680]  bit_cursor+0x3ac/0x500
[   23.763687]  fbcon_cursor+0xec/0x11c
[   23.763694]  hide_cursor+0x3c/0xc0
[   23.763708]  redraw_screen+0x128/0x240
[   23.763717]  do_bind_con_driver.isra.0+0x2c8/0x39c
[   23.763726]  do_take_over_console+0x140/0x200
[   23.763736]  do_fbcon_takeover+0x6c/0xe4
[   23.763742]  fbcon_fb_registered+0x1e4/0x1f0
[   23.763749]  register_framebuffer+0x214/0x310
[   23.763761]  __drm_fb_helper_initial_config_and_unlock+0x33c/0x534 [drm_kms_helper]
[   23.763837]  drm_fb_helper_initial_config+0x4c/0x60 [drm_kms_helper]
[   23.763912]  drm_fbdev_client_hotplug+0xc4/0x150 [drm_kms_helper]
[   23.763987]  drm_fbdev_generic_setup+0x90/0x154 [drm_kms_helper]
[   23.764061]  rcar_du_probe+0x154/0x184 [rcar_du_drm]
[   23.764103]  platform_probe+0x68/0xe0
[   23.764115]  really_probe+0xbc/0x2e0
[   23.764122]  __driver_probe_device+0x78/0xe0
[   23.764129]  driver_probe_device+0xd8/0x15c
[   23.764136]  __driver_attach+0x94/0x19c
[   23.764143]  bus_for_each_dev+0x70/0xd0
[   23.764149]  driver_attach+0x24/0x30
[   23.764155]  bus_add_driver+0x154/0x20c
[   23.764161]  driver_register+0x78/0x130
[   23.764168]  __platform_driver_register+0x28/0x34
[   23.764176]  rcar_du_platform_driver_init+0x20/0x1000 [rcar_du_drm]

Cheers,
Biju

Subject: [PATCH v2 5/6] drm/fb-helper: Schedule deferred-I/O worker after
writing to framebuffer

Schedule the deferred-I/O worker instead of the damage worker after
writing to the fbdev framebuffer. The deferred-I/O worker then performs
the dirty-fb update. The fbdev emulation will initialize deferred I/O
for all drivers that require damage updates. It is therefore a valid
assumption that the deferred-I/O worker is present.

It would be possible to perform the damage handling directly from within
the write operation. But doing this could increase the overhead of the
write or interfere with a concurrently scheduled deferred-I/O worker.
Instead, scheduling the deferred-I/O worker with its regular delay of
50 ms removes load off the write operation and allows the deferred-I/O
worker to handle multiple write operations that arrived during the delay
time window.

v2:
	* keep drm_fb_helper_damage() (Daniel)
	* use fb_deferred_io_schedule_flush() (Daniel)
	* clarify comments (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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