[v3,3/7] drm/bridge_connector: rely on drm_kms_helper_poll_* for HPD enablement

[Marek Szyprowski]

Hi Neil,

On 12.01.2023 10:35, Neil Armstrong wrote:
> On 11/01/2023 13:41, Marek Szyprowski wrote:
>> On 02.11.2022 19:07, Dmitry Baryshkov wrote:
>>> Use drm_connector's helpers enable_hpd and disable_hpd to enable and
>>> disable HPD automatically by the means of drm_kms_helper_poll_*
>>> functions. As the drm_bridge_connector_enable_hpd() and
>>> drm_bridge_connector_disable_hpd() functions are now unused, replace
>>> them with stubs to ease driver migration.
>>>
>>> Enabling the HPD from drm_bridge_connector_init() can happen too early,
>>> before the driver is prepared to handle HPD events. As the
>>> drm_bridge_connector_enable_hpd() is empty anyway, drop this call
>>> anyway.
>>>
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>> ---
>>
>> This patch, merged to recent linux-next as commit 92d755d8f13b
>> ("drm/bridge_connector: rely on drm_kms_helper_poll_* for HPD
>> enablement"), triggers the following warning on all my Amlogic Meson
>> based boards:
>>
>> ------------[ cut here ]------------
>> Hot plug detection already enabled
>> WARNING: CPU: 2 PID: 285 at drivers/gpu/drm/drm_bridge.c:1257
>> drm_bridge_hpd_enable+0x90/0xa0
>> Modules linked in: snd_soc_meson_axg_frddr snd_soc_meson_axg_fifo
>> dwmac_generic panfrost(+) reset_meson_audio_arb(+) drm_shmem_helper
>> meson_dw_hdmi(+) dw_hdmi rc_odroid drm_display_helper meson_ir(+)
>> gpu_sched meson_rng rng_core meson_gxbb_wdt crct10dif_ce dwmac_meson8b
>> stmmac_platform snd_soc_meson_axg_sound_card snd_soc_meson_card_utils
>> mdio_mux_meson_g12a stmmac meson_drm pwm_meson pcs_xpcs meson_canvas
>> snd_soc_meson_axg_tdm_interface rtc_meson_vrtc
>> snd_soc_meson_axg_tdm_formatter nvmem_meson_efuse display_connector
>> CPU: 2 PID: 285 Comm: systemd-udevd Not tainted 6.1.0-rc6+ #13236
>> Hardware name: Hardkernel ODROID-C4 (DT)
>> pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> pc : drm_bridge_hpd_enable+0x90/0xa0
>> lr : drm_bridge_hpd_enable+0x90/0xa0
>> ...
>> Call trace:
>>    drm_bridge_hpd_enable+0x90/0xa0
>>    _drm_bridge_connector_enable_hpd+0x24/0x34
>
> Weird because _drm_bridge_connector_enable_hpd() has been removed with
> 4c00ac500d0e ("drm/bridge_connector: drop 
> drm_bridge_connector_en/disable_hpd()")

The above log has been captured at commit 92d755d8f13b during bisecting, 
so 4c00ac500d0e is not applied yet. Maybe I should have mention that. 
The issue on top of linux-next is similar.

>
>>  drm_kms_helper_poll_enable.part.0+0x50/0xd0
>
> It seems drm_kms_helper_poll_enable is called again by
> drm_helper_probe_single_connector_modes() because poll_running isn't set.
>
> Can you try with this change:

This fixes the issue on top of linux next-20230112. Thanks! Feel free to 
add if you plan to submit it as a formal patch:

Reported-by: Marek Szyprowski <m.szyprowski at samsung.com>

Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland