drm: Bogus WARN() in drm_atomic_helper_update_legacy_modeset_state() ?
Thierry Reding
thierry.reding at gmail.com
Thu Nov 12 05:34:11 PST 2015
On Thu, Nov 12, 2015 at 06:49:38PM +0800, Mark yao wrote:
> On 2015年11月12日 18:36, Liviu Dudau wrote:
> >On Thu, Nov 12, 2015 at 04:32:33PM +0800, Mark yao wrote:
> >> On 2015年11月10日 23:01, Liviu Dudau wrote:
> >>
> >> Hello,
> >>
> >> When booting my Juno board with the HDLCD driver that I have converted to
> >> atomic operations I'm getting the following warning:
> >>
> >> ------------[ cut here ]------------
> >> WARNING: at /work/repositories/kernel/drivers/gpu/drm/drm_atomic_helper.c:674
> >> Modules linked in: hdlcd(+) clk_scpi
> >>
> >> CPU: 3 PID: 1375 Comm: systemd-udevd Not tainted 4.3.0-next-20151109+ #5
> >> Hardware name: ARM Juno development board (r0) (DT)
> >> task: ffffffc974888b00 ti: ffffffc9755dc000 task.ti: ffffffc9755dc000
> >> PC is at drm_atomic_helper_update_legacy_modeset_state+0x204/0x20c
> >> LR is at drm_atomic_helper_commit_modeset_disables+0x1c0/0x394
> >> pc : [<ffffffc0003e6d18>] lr : [<ffffffc0003e8214>] pstate: 20000145
> >> sp : ffffffc9755df430
> >> x29: ffffffc9755df430 x28: ffffffc975703600
> >> x27: 0000000000000000 x26: ffffffc976253960
> >> x25: ffffffc976254040 x24: ffffffc000819000
> >> x23: ffffffc000689ea0 x22: ffffffc976251800
> >> x21: ffffffc976251800 x20: 0000000000000000
> >> x19: ffffffc9766b1f80 x18: 00000000715fe015
> >> x17: 0000007fb4b855b0 x16: 0000000000000220
> >> x15: 0000000000000001 x14: 0ffffffffffffffe
> >> x13: 0000000000000008 x12: 0101010101010101
> >> x11: ffffffc000964000 x10: ffffffc0009d2000
> >> x9 : 0000000000000000 x8 : ffffffc97ff5f700
> >> x7 : ffffffc97566cb80 x6 : ffffffc9766b1700
> >> x5 : ffffffc975665100 x4 : 0000000000000000
> >> x3 : ffffffc976253960 x2 : ffffffc97566cd00
> >> x1 : ffffffc976253900 x0 : 0000000000000000
> >>
> >> ---[ end trace 9fe289f798e7178e ]---
> >> Call trace:
> >> [<ffffffc0003e6d18>] drm_atomic_helper_update_legacy_modeset_state+0x204/0x20c
> >> [<ffffffc0003e8214>] drm_atomic_helper_commit_modeset_disables+0x1c0/0x394
> >> [<ffffffc0003e84c8>] drm_atomic_helper_commit+0xe0/0x150
> >> [<ffffffc00040bcc0>] drm_atomic_commit+0x40/0x6c
> >> [<ffffffc0003e92c0>] restore_fbdev_mode+0x294/0x2d4
> >> [<ffffffc0003eb6ec>] drm_fb_helper_restore_fbdev_mode_unlocked+0x34/0x8c
> >> [<ffffffc0003eb770>] drm_fb_helper_set_par+0x2c/0x58
> >> [<ffffffc000378048>] fbcon_init+0x4d4/0x534
> >> [<ffffffc0003b44f4>] visual_init+0xac/0x104
> >> [<ffffffc0003b63f8>] do_bind_con_driver+0x16c/0x398
> >> [<ffffffc0003b6968>] do_take_over_console+0xd8/0x1f4
> >> [<ffffffc00037811c>] do_fbcon_takeover+0x74/0xf8
> >> [<ffffffc00037c5cc>] fbcon_event_notify+0x8a4/0x8f8
> >> [<ffffffc0000d19f0>] notifier_call_chain+0x4c/0x88
> >> [<ffffffc0000d1d78>] __blocking_notifier_call_chain+0x44/0x74
> >> [<ffffffc0000d1dbc>] blocking_notifier_call_chain+0x14/0x1c
> >> [<ffffffc00037d614>] fb_notifier_call_chain+0x1c/0x24
> >> [<ffffffc00037f8a8>] register_framebuffer+0x1c0/0x2ac
> >> [<ffffffc0003eb9f8>] drm_fb_helper_initial_config+0x25c/0x3ec
> >> [<ffffffc0003ec28c>] drm_fbdev_cma_init+0x98/0x134
> >> [<ffffffbffc006780>] hdlcd_drm_bind+0x180/0x498 [hdlcd]
> >> [<ffffffc0004158e0>] try_to_bring_up_master.part.5+0xd4/0x118
> >> [<ffffffc0004159e8>] component_master_add_with_match+0xc4/0x148
> >> [<ffffffc000415a7c>] component_master_add+0x10/0x18
> >> [<ffffffbffc0065ec>] hdlcd_probe+0x14/0x28 [hdlcd]
> >> [<ffffffc00041c504>] platform_drv_probe+0x54/0xc0
> >> [<ffffffc00041a9b0>] driver_probe_device+0x1ec/0x2e8
> >> [<ffffffc00041ab48>] __driver_attach+0x9c/0xa0
> >> [<ffffffc000418bcc>] bus_for_each_dev+0x58/0x98
> >> [<ffffffc00041a41c>] driver_attach+0x20/0x28
> >> [<ffffffc00041a058>] bus_add_driver+0x1c8/0x22c
> >> [<ffffffc00041b3d0>] driver_register+0x68/0x108
> >> [<ffffffc00041c408>] __platform_driver_register+0x4c/0x54
> >> [<ffffffbffc00b018>] hdlcd_init+0x18/0x30 [hdlcd]
> >> [<ffffffc00008293c>] do_one_initcall+0x90/0x1a8
> >> [<ffffffc0001424dc>] do_init_module+0x60/0x1c8
> >> [<ffffffc00011d364>] load_module+0x1554/0x1c98
> >> [<ffffffc00011dc64>] SyS_finit_module+0x7c/0x88
> >> [<ffffffc000085cb0>] el0_svc_naked+0x24/0x28
> >>
> >>
> >> The line that triggers the warning is:
> >>
> >> 674: WARN_ON(!connector->encoder->crtc);
> >>
> >> As far as I can see the encoder->crtc value is being set to a non-NULL value only
> >> in two places:
> >> - in drm_atomic_helper_update_legacy_modeset_state() after WARN_ON()
> >> encoder->crtc = connector->state->crtc;
> >> - in drm_crtc_helper_set_config(drm_mode_set *set):
> >> encoder->crtc = new_crtc;
> >>
> >> Nothing in the call path from drm_atomic_commit() calls crtc_funcs->set_config() or
> >> drm_crtc_helper_set_config() directly, so the question is if this WARN() is actually
> >> valid.
> >>
> >> Call path from drm_atomic_commit:
> >>
> >> drm_atomic_helper_commit()
> >> - drm_atomic_helper_prepare_planes()
> >> - drm_atomic_helper_swap_state()
> >> - drm_atomic_helper_commit_modeset_disables()
> >> - disable_outputs()
> >> - drm_atomic_helper_update_legacy_modeset_state()
> >> - WARN_ON(!connector->encoder->crtc)
> >>
> >> Best regards,
> >> Liviu
> >>
> >>
> >> Hi Liviu
> >> I solved this problem by following change, you can check if your driver do the same things:
> >> drivers/gpu/drm/bridge/dw_hdmi.c:
> >> - hdmi->connector.encoder = encoder;
> >> +// hdmi->connector.encoder = encoder;
> >>
> >> drm_mode_connector_attach_encoder(&hdmi->connector, encoder);
> >>
> >> I found some other drivers set connector.encoder before drm_mode_connector_attach_encoder, some are not.
> >>
> >> drm_mode_connector_attach_encoder already describe the link of connector and encoder,
> >> so I think "connector.encoder = encoder" is not needed, is that right?
> >I'll have a look, thanks for pointing this. However, my setup uses the tda998x driver for encoder, so I will
> >have to go look there rather than in my driver.
> >
> >Best regards,
> >Liviu
> >
> >> Thanks.
> >>
> >> --
> >> Ｍark Yao
> Hi Liviu
> drivers/gpu/drm/i2c/tda998x_drv.c do the same things:
> priv->connector.encoder = &priv->encoder;
> drm_mode_connector_attach_encoder(&priv->connector, &priv->encoder);
>
> I believe must be same problem.
Oh, I hadn't noticed this subthread, but you came to the same conclusion
as I did. I have the below local change, which I think might be good to
have given that there are at least two drivers that got this wrong.
Thierry
--- >8 ---
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 24c5434abd1c..56d53106b32d 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -4983,6 +4983,20 @@ int drm_mode_connector_attach_encoder(struct drm_connector *connector,
{
int i;
+ /*
+ * In the past, drivers have attempted to model the static association
+ * of connector to encoder in simple connector/encoder devices using a
+ * direct assignment of connector->encoder = encoder. This connection
+ * is a logical one and the responsibility of the core, so drivers are
+ * expected not to mess with this.
+ *
+ * Note that the error return should've been enough here, but a large
+ * majority of drivers ignores the return value, so add in a big WARN
+ * to get people's attention.
+ */
+ if (WARN_ON(connector->encoder))
+ return -EINVAL;
+
for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
if (connector->encoder_ids[i] == 0) {
connector->encoder_ids[i] = encoder->base.id;
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