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Wed, 11 Dec 2024 02:52:06 -0800 (PST) Received: from linaro.org ([82.76.168.176]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-387824a4e98sm1006870f8f.34.2024.12.11.02.52.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Dec 2024 02:52:05 -0800 (PST) Date: Wed, 11 Dec 2024 12:52:03 +0200 From: Abel Vesa To: Dmitry Baryshkov Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Karol Herbst , Lyude Paul , Danilo Krummrich , Jani Nikula , Rodrigo Vivi , Joonas Lahtinen , Tvrtko Ursulin , Rob Clark , Abhinav Kumar , Sean Paul , Marijn Suijten , Bjorn Andersson , Konrad Dybcio , Johan Hovold , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, nouveau@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org Subject: Re: [PATCH RFC 4/4] drm/msm/dp: Add support for LTTPR handling Message-ID: References: <20241031-drm-dp-msm-add-lttpr-transparent-mode-set-v1-0-cafbb9855f40@linaro.org> <20241031-drm-dp-msm-add-lttpr-transparent-mode-set-v1-4-cafbb9855f40@linaro.org> <6lpeexb5menpwrzcnmr367x4lmhvzyovhdybn54mnwk55ieehy@mos4oso67boo> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mailman-Approved-At: Thu, 12 Dec 2024 13:11:29 +0000 X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 24-12-11 11:55:54, Dmitry Baryshkov wrote: > On Wed, Dec 11, 2024 at 11:08:16AM +0200, Abel Vesa wrote: > > On 24-10-31 18:54:25, Dmitry Baryshkov wrote: > > > On Thu, Oct 31, 2024 at 05:12:48PM +0200, Abel Vesa wrote: > > > > Link Training Tunable PHY Repeaters (LTTPRs) are defined in DisplayPort > > > > 1.4a specification. As the name suggests, these PHY repeaters are > > > > capable of adjusting their output for link training purposes. > > > > > > > > The msm DP driver is currently lacking any handling of LTTPRs. > > > > This means that if at least one LTTPR is found between DPTX and DPRX, > > > > the link training would fail if that LTTPR was not already configured > > > > in transparent mode. > > > > > > It might be nice to mention what is the transparent mode, especially for > > > those who do not have the standard at hand. > > > > Sorry for the late reply. > > > > Will do in the next version. > > > > > > > > > The section 3.6.6.1 from the DisplayPort v2.0 specification mandates > > > > that before link training with the LTTPR is started, the DPTX may place > > > > the LTTPR in non-transparent mode by first switching to transparent mode > > > > and then to non-transparent mode. This operation seems to be needed only > > > > on first link training and doesn't need to be done again until device is > > > > unplugged. > > > > > > > > It has been observed on a few X Elite-based platforms which have > > > > such LTTPRs in their board design that the DPTX needs to follow the > > > > procedure described above in order for the link training to be successful. > > > > > > > > So add support for reading the LTTPR DPCD caps to figure out the number > > > > of such LTTPRs first. Then, for platforms (or Type-C dongles) that have > > > > at least one such an LTTPR, set its operation mode to transparent mode > > > > first and then to non-transparent, just like the mentioned section of > > > > the specification mandates. > > > > > > > > Signed-off-by: Abel Vesa > > > > --- > > > > drivers/gpu/drm/msm/dp/dp_display.c | 25 +++++++++++++++++++++++++ > > > > 1 file changed, 25 insertions(+) > > > > > > > > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c > > > > index f01980b0888a40b719d3958cb96c6341feada077..5d3d318d7b87ce3bf567d8b7435931d8e087f713 100644 > > > > --- a/drivers/gpu/drm/msm/dp/dp_display.c > > > > +++ b/drivers/gpu/drm/msm/dp/dp_display.c > > > > @@ -107,6 +107,8 @@ struct dp_display_private { > > > > struct dp_event event_list[DP_EVENT_Q_MAX]; > > > > spinlock_t event_lock; > > > > > > > > + u8 lttpr_caps[DP_LTTPR_COMMON_CAP_SIZE]; > > > > + > > > > bool wide_bus_supported; > > > > > > > > struct dp_audio *audio; > > > > @@ -367,12 +369,35 @@ static int dp_display_send_hpd_notification(struct dp_display_private *dp, > > > > return 0; > > > > } > > > > > > > > +static void dp_display_lttpr_init(struct dp_display_private *dp) > > > > +{ > > > > + int lttpr_count; > > > > + > > > > + if (drm_dp_read_lttpr_common_caps(dp->aux, dp->panel->dpcd, > > > > + dp->lttpr_caps)) > > > > + return; > > > > + > > > > + lttpr_count = drm_dp_lttpr_count(dp->lttpr_caps); > > > > + > > > > + if (lttpr_count) { > > > > + drm_dp_lttpr_set_transparent_mode(dp->aux, true); > > > > + > > > > + if (lttpr_count > 0) { > > > > + if (drm_dp_lttpr_set_transparent_mode(dp->aux, false) != 1) > > > > + drm_dp_lttpr_set_transparent_mode(dp->aux, true); > > > > + } > > > > + } > > > > +} > > > > + > > > > static int dp_display_process_hpd_high(struct dp_display_private *dp) > > > > { > > > > struct drm_connector *connector = dp->dp_display.connector; > > > > const struct drm_display_info *info = &connector->display_info; > > > > int rc = 0; > > > > > > > > + if (!dp->dp_display.is_edp) > > > > + dp_display_lttpr_init(dp); > > > > > > Why is it limited to non-eDP cases only. > > > > In case of eDP, I don't think that there will ever by a case that will > > need an LTTPR in between the eDP PHY and the actual panel. It just > > doesn't make sense. > > > > IIUC, the LTTPRs, since are Training Tunnable capable, they help when > > the physical link between the PHY and the sink can differ based on > > different dongles and cables. This is obviously not applicable to eDP. > > I think I just have a different paradigm: if the driver explicitly skips > calling a function in some codepath, I assume that the usecase it broken > or expected not to work (e.g. I read your patch like: LTTPR is expected > not to work in eDP). If you would prefer to keep two separate code > paths, please add a comment like 'we don't expect LTTPRs in eDP > usecase`. Fair point. But maybe I should drop the non-eDP condition entirely, since the LTTPR count will read 0 and then the new helper (which will be called drm_dp_lttpr_init() and will handle the disable->enable->disable dance, just like you requested) will bail early if LTTPR count is 0. That way should be more clean, IMO. > > > > > + > > > > rc = dp_panel_read_sink_caps(dp->panel, connector); > > > > if (rc) > > > > goto end; > > > > > > > > -- > > > > 2.34.1 > > > > > > > > > > -- > > > With best wishes > > > Dmitry > > -- > With best wishes > Dmitry