linux-kernel - Re: [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

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Date:   Tue, 22 Nov 2016 10:07:53 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Archit Taneja <architt@...eaurora.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 2/3] drm/bridge: adv7511: Add 200ms delay on power-on

On Tue, Nov 22, 2016 at 9:38 AM, John Stultz <john.stultz@...aro.org> wrote:
>
> Interestingly, without the msleep added in this patch, removing the
> wait_event_interruptible_timeout() method in adv7511_wait_for_edid()
> and using the polling loop seems to make things just as reliable. So
> maybe something is off with the irq handling here instead?

Ahhhh.. So I think the trouble here is the that when we fail waiting
for the irq, the backtrace is as follows:

[    8.318654] [<ffffff8008087c28>] dump_backtrace+0x0/0x1a0
[    8.318661] [<ffffff8008087ddc>] show_stack+0x14/0x20
[    8.318671] [<ffffff80084344f0>] dump_stack+0x90/0xb0
[    8.318680] [<ffffff8008534650>] adv7511_get_edid_block+0x2c8/0x320
[    8.318687] [<ffffff80085214a8>] drm_do_get_edid+0x78/0x280
[    8.318693] [<ffffff8008534728>] adv7511_get_modes+0x80/0xd8
[    8.318700] [<ffffff8008534794>] adv7511_connector_get_modes+0x14/0x20
[    8.318710] [<ffffff8008500a54>]
drm_helper_probe_single_connector_modes+0x2bc/0x500
[    8.318718] [<ffffff800850e400>] drm_fb_helper_hotplug_event+0x130/0x188
[    8.318726] [<ffffff800850ee68>] drm_fbdev_cma_hotplug_event+0x10/0x20
[    8.318733] [<ffffff8008535718>] kirin_fbdev_output_poll_changed+0x20/0x58
[    8.318740] [<ffffff8008500cc0>] drm_kms_helper_hotplug_event+0x28/0x38
[    8.318748] [<ffffff80085010d8>] drm_helper_hpd_irq_event+0x138/0x180
[    8.318754] [<ffffff8008533850>] adv7511_irq_process+0x78/0xd8
[    8.318761] [<ffffff80085338c4>] adv7511_irq_handler+0x14/0x28
[    8.318769] [<ffffff8008100060>] irq_thread_fn+0x28/0x68
[    8.318775] [<ffffff8008100350>] irq_thread+0x128/0x1e8
[    8.318782] [<ffffff80080d2e68>] kthread+0xd0/0xe8
[    8.318788] [<ffffff8008082e80>] ret_from_fork+0x10/0x50

So we're actually in irq handling the hotplug interrupt, which is why
we never get the irq notification when the edid is read.

I suspect we need to use a workqueue to do the hotplug handling out of irq.

thanks
-john