From: Abhinav Kumar <quic_abhinavk@quicinc.com>
To: Douglas Anderson <dianders@chromium.org>,
<dri-devel@lists.freedesktop.org>,
Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: <linux-tegra@vger.kernel.org>,
Mikko Perttunen <mperttunen@nvidia.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Thierry Reding <thierry.reding@gmail.com>,
Ankit Nautiyal <ankit.k.nautiyal@intel.com>,
Daniel Vetter <daniel@ffwll.ch>, David Airlie <airlied@gmail.com>,
Imre Deak <imre.deak@intel.com>,
Jani Nikula <jani.nikula@intel.com>,
Maxime Ripard <mripard@kernel.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drm/dp: Clarify that wait_hpd_asserted() is not optional for panels
Date: Tue, 19 Mar 2024 11:26:19 -0700 [thread overview]
Message-ID: <b9e1a57d-0bdd-45f4-f589-792f8ea82835@quicinc.com> (raw)
In-Reply-To: <20240319111432.1.I521dad0693cc24fe4dd14cba0c7048d94f5b6b41@changeid>
On 3/19/2024 11:14 AM, Douglas Anderson wrote:
> In response to my patch removing the "wait for HPD" logic at the
> beginning of the MSM DP transfer() callback [1], we had some debate
> about what the "This is an optional function" meant in the
> documentation of the wait_hpd_asserted() callback. Let's clarify.
>
> As talked about in the MSM DP patch [1], before wait_hpd_asserted()
> was introduced there was no great way for panel drivers to wait for
> HPD in the case that the "built-in" HPD signal was used. Panel drivers
> could only wait for HPD if a GPIO was used. At the time, we ended up
> just saying that if we were using the "built-in" HPD signal that DP
> AUX controllers needed to wait for HPD themselves at the beginning of
> their transfer() callback. The fact that the wait for HPD at the
> beginning of transfer() was awkward/problematic was the whole reason
> wait_hpd_asserted() was added.
>
> Let's make it obvious that if a DP AUX controller implements
> wait_hpd_asserted() that they don't need a loop waiting for HPD at the
> start of their transfer() function. We'll still allow DP controllers
> to work the old way but mark it as deprecated.
>
> [1] https://lore.kernel.org/r/20240315143621.v2.3.I535606f6d4f7e3e5588bb75c55996f61980183cd@changeid
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> I would consider changing the docs to say that implementing
> wait_hpd_asserted() is actually _required_ for any DP controllers that
> want to support eDP panels parented on the DP AUX bus. The issue is
> that one DP controller (tegra/dpaux.c, found by looking for those that
> include display/drm_dp_aux_bus.h) does populate the DP AUX bus but
> doesn't implement wait_hpd_asserted(). I'm actually not sure how/if
> this work on tegra since I also don't see any delay loop for HPD in
> tegra's transfer() callback. For now, I've left wait_hpd_asserted() as
> optional and described the old/deprecated way things used to work
> before wait_hpd_asserted().
>
> include/drm/display/drm_dp_helper.h | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
Thanks for the change,
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
next prev parent reply other threads:[~2024-03-19 18:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-19 18:14 [PATCH] drm/dp: Clarify that wait_hpd_asserted() is not optional for panels Douglas Anderson
2024-03-19 18:26 ` Abhinav Kumar [this message]
2024-03-19 18:35 ` Dmitry Baryshkov
2024-03-19 19:02 ` Abhinav Kumar
2024-03-19 20:16 ` Dmitry Baryshkov
2024-03-19 20:38 ` Abhinav Kumar
2024-03-19 20:54 ` Dmitry Baryshkov
2024-03-19 21:00 ` Doug Anderson
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=b9e1a57d-0bdd-45f4-f589-792f8ea82835@quicinc.com \
--to=quic_abhinavk@quicinc.com \
--cc=airlied@gmail.com \
--cc=ankit.k.nautiyal@intel.com \
--cc=daniel@ffwll.ch \
--cc=dianders@chromium.org \
--cc=dmitry.baryshkov@linaro.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=imre.deak@intel.com \
--cc=jani.nikula@intel.com \
--cc=jonathanh@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tegra@vger.kernel.org \
--cc=mperttunen@nvidia.com \
--cc=mripard@kernel.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 read-only IMAP folder(s) and NNTP newsgroup(s).