From: Marek Vasut <marex@denx.de>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: "Alexandre Torgue" <alexandre.torgue@st.com>,
"Philippe Cornu" <philippe.cornu@st.com>,
dri-devel@lists.freedesktop.org,
"Yannick Fertré" <yannick.fertre@st.com>,
linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org,
"Benjamin Gaignard" <benjamin.gaignard@st.com>
Subject: Re: [PATCH] drm/stm: Enable RPM during fbdev registration
Date: Thu, 5 Nov 2020 10:45:06 +0100 [thread overview]
Message-ID: <e7bdd094-2109-34f1-77dc-165ff2706d20@denx.de> (raw)
In-Reply-To: <20201105093945.GS401619@phenom.ffwll.local>
On 11/5/20 10:39 AM, Daniel Vetter wrote:
> On Wed, Nov 04, 2020 at 01:52:00PM +0100, Marek Vasut wrote:
>> Enable runtime PM before registering the fbdev emulation and disable it
>> afterward, otherwise register access to the LTDC IP during the fbdev
>> emulation registration might hang the system.
>>
>> The problem happens because RPM is activated at the end of ltdc_load(),
>> but the fbdev emulation registration happens only after that, and ends
>> up calling ltdc_crtc_mode_set_nofb(), which checks whether RPM is active
>> and only if it is not active, calls pm_runtime_get_sync() to enable the
>> clock and so on. If the clock are not enabled, any register access in
>> ltdc_crtc_mode_set_nofb() could hang the platform completely.
>>
>> This patch makes sure that ltdc_crtc_mode_set_nofb() is called within
>> pm_runtime_get_sync(), so with clock enabled.
[...]
> This looks like you're papering over a bug in your modeset code. If
> userspace later on does a setpar on the fbdev chardev, the exact same
> thing could happen. You need to fix your modeset code to avoid this, not
> sprinkle temporary rpm_get/put all over some top level entry points,
> because you can't even patch those all.
I have a feeling all those pm_runtime_active() checks in the driver
might be the root cause of this ? I wonder why the code doesn't use
pm_runtime_{get,put}_sync() only when accessing registers. Thoughts?
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next prev parent reply other threads:[~2020-11-05 9:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-04 12:52 [PATCH] drm/stm: Enable RPM during fbdev registration Marek Vasut
2020-11-05 9:39 ` Daniel Vetter
2020-11-05 9:45 ` Marek Vasut [this message]
2020-11-06 16:13 ` Yannick FERTRE
2020-11-06 16:23 ` Marek Vasut
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