From: Doug Anderson <dianders@chromium.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Andrzej Hajda <a.hajda@samsung.com>,
Neil Armstrong <narmstrong@baylibre.com>,
Jonas Karlman <jonas@kwiboo.se>,
Jernej Skrabec <jernej.skrabec@siol.net>,
Sam Ravnborg <sam@ravnborg.org>,
Linus W <linus.walleij@linaro.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Rob Clark <robdclark@chromium.org>,
Stephen Boyd <swboyd@chromium.org>,
Steev Klimaszewski <steev@kali.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>,
Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@linux.ie>,
Thierry Reding <thierry.reding@gmail.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 12/12] drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare / prepare
Date: Wed, 14 Apr 2021 18:22:57 -0700 [thread overview]
Message-ID: <CAD=FV=X=XixXONS9D4CRxku4VuKa2pYniSjzSoX_NXkDW-J15g@mail.gmail.com> (raw)
In-Reply-To: <YHePsQgqOau1V5lD@pendragon.ideasonboard.com>
Hi,
On Wed, Apr 14, 2021 at 5:58 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Doug,
>
> Thank you for the patch.
>
> On Fri, Apr 02, 2021 at 03:28:46PM -0700, Douglas Anderson wrote:
> > Unpreparing and re-preparing a panel can be a really heavy
> > operation. Panels datasheets often specify something on the order of
> > 500ms as the delay you should insert after turning off the panel
> > before turning it on again. In addition, turning on a panel can have
> > delays on the order of 100ms - 200ms before the panel will assert HPD
> > (AKA "panel ready"). The above means that we should avoid turning a
> > panel off if we're going to turn it on again shortly.
> >
> > The above becomes a problem when we want to read the EDID of a
> > panel. The way that ordering works is that userspace wants to read the
> > EDID of the panel _before_ fully enabling it so that it can set the
> > initial mode correctly. However, we can't read the EDID until we power
> > it up. This leads to code that does this dance (like
> > ps8640_bridge_get_edid()):
> >
> > 1. When userspace requests EDID / the panel modes (through an ioctl),
> > we power on the panel just enough to read the EDID and then power
> > it off.
> > 2. Userspace then turns the panel on.
> >
> > There's likely not much time between step #1 and #2 and so we want to
> > avoid powering the panel off and on again between those two steps.
> >
> > Let's use Runtime PM to help us. We'll move the existing prepare() and
> > unprepare() to be runtime resume() and runtime suspend(). Now when we
> > want to prepare() or unprepare() we just increment or decrement the
> > refcount. We'll default to a 1 second autosuspend delay which seems
> > sane given the typical delays we see for panels.
> >
> > A few notes:
> > - It seems the existing unprepare() and prepare() are defined to be
> > no-ops if called extra times. We'll preserve that behavior.
>
> The prepare and unprepare calls are supposed to be balanced, which
> should allow us to drop this check. Do you have a reason to suspect that
> it may not be the case ?
No, it was just code inspection. The old code definitely made an
effort to make enable of an already enabled panel a no-op and disable
of an already disabled panel a no-op. This is even before my
(somewhat) recent patch to make things timing based, though I did
touch the code.
Can I maybe suggest that getting rid of the extra check should be a
separate patch after this one? Then if it breaks someone it's easy to
just revert that one and we can still keep the runtime pm?
> > - This is a slight change in the ABI of simple panel. If something was
> > absolutely relying on the unprepare() to happen instantly that
> > simply won't be the case anymore. I'm not aware of anyone relying on
> > that behavior, but if there is someone then we'll need to figure out
> > how to enable (or disable) this new delayed behavior selectively.
> > - In order for this to work we now have a hard dependency on
> > "PM". From memory this is a legit thing to assume these days and we
> > don't have to find some fallback to keep working if someone wants to
> > build their system without "PM".
>
> Sounds fine to me.
>
> The code looks good to me. Possibly with the prepared check removed,
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Thanks!
next prev parent reply other threads:[~2021-04-15 1:23 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-02 22:28 [PATCH v3 00/12] drm: Fix EDID reading on ti-sn65dsi86 Douglas Anderson
2021-04-02 22:28 ` [PATCH v3 01/12] drm/bridge: Fix the stop condition of drm_bridge_chain_pre_enable() Douglas Anderson
2021-04-05 0:49 ` Laurent Pinchart
2021-04-15 1:19 ` Doug Anderson
2021-04-15 1:56 ` Laurent Pinchart
2021-04-15 14:48 ` Doug Anderson
2021-04-02 22:28 ` [PATCH v3 02/12] drm/bridge: ti-sn65dsi86: Simplify refclk handling Douglas Anderson
2021-04-02 22:28 ` [PATCH v3 03/12] drm/bridge: ti-sn65dsi86: Remove incorrectly tagged kerneldoc comment Douglas Anderson
2021-04-05 0:50 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 04/12] drm/bridge: ti-sn65dsi86: Reorder remove() Douglas Anderson
2021-04-05 0:52 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 05/12] drm/bridge: ti-sn65dsi86: Move drm_panel_unprepare() to post_disable() Douglas Anderson
2021-04-05 0:58 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 06/12] drm/bridge: ti-sn65dsi86: Get rid of the useless detect() function Douglas Anderson
2021-04-05 0:58 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 07/12] drm/bridge: ti-sn65dsi86: Remove extra call: drm_connector_update_edid_property() Douglas Anderson
2021-04-05 1:01 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 08/12] drm/bridge: ti-sn65dsi86: Power things properly for reading the EDID Douglas Anderson
2021-04-02 22:28 ` [PATCH v3 09/12] drm/bridge: ti-sn65dsi86: Fail aux transfers right away if not powered Douglas Anderson
2021-04-02 22:28 ` [PATCH v3 10/12] drm/bridge: ti-sn65dsi86: Read the EDID only if refclk was provided Douglas Anderson
2021-04-05 1:04 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 11/12] drm/bridge: ti-sn65dsi86: Print an error if we fallback to panel modes Douglas Anderson
2021-04-05 1:04 ` Laurent Pinchart
2021-04-02 22:28 ` [PATCH v3 12/12] drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare / prepare Douglas Anderson
2021-04-15 0:58 ` Laurent Pinchart
2021-04-15 1:22 ` Doug Anderson [this message]
2021-04-15 1:30 ` Laurent Pinchart
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAD=FV=X=XixXONS9D4CRxku4VuKa2pYniSjzSoX_NXkDW-J15g@mail.gmail.com' \
--to=dianders@chromium.org \
--cc=a.hajda@samsung.com \
--cc=airlied@linux.ie \
--cc=bjorn.andersson@linaro.org \
--cc=daniel@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=jernej.skrabec@siol.net \
--cc=jonas@kwiboo.se \
--cc=laurent.pinchart@ideasonboard.com \
--cc=linus.walleij@linaro.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maarten.lankhorst@linux.intel.com \
--cc=narmstrong@baylibre.com \
--cc=robdclark@chromium.org \
--cc=sam@ravnborg.org \
--cc=stanislav.lisovskiy@intel.com \
--cc=steev@kali.org \
--cc=swboyd@chromium.org \
--cc=thierry.reding@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).