If an eDP panel is not powered on then any attempts to talk to it over
the DP AUX channel will timeout. Unfortunately these attempts may be
quite slow. Userspace can initiate these attempts either via a
/dev/drm_dp_auxN device or via the created i2c device.
Making the DP AUX drivers timeout faster is a difficult proposition.
In theory we could just poll the panel's HPD line in the AUX transfer
function and immediately return an error there. However, this is
easier said than done. For one thing, there's no hard requirement to
hook the HPD line up for eDP panels and it's OK to just delay a fixed
amount. For another thing, the HPD line may not be fast to probe. On
parade-ps8640 we need to wait for the bridge chip's firmware to boot
before we can get the HPD line and this is a slow process.
The fact that the transfers are taking so long to timeout is causing
real problems. The open source fwupd daemon sometimes scans DP busses
looking for devices whose firmware need updating. If it happens to
scan while a panel is turned off this scan can take a long time. The
fwupd daemon could try to be smarter and only scan when eDP panels are
turned on, but we can also improve the behavior in the kernel.
Let's let eDP panels drivers specify that a panel is turned off and
then modify the common AUX transfer code not to attempt a transfer in
this case.
Tested-by: Steev Klimaszewski <steev@kali.org>
Reviewed-by: Hsin-Yi Wang <hsinyi@chromium.org>
Tested-by: Eizan Miyamoto <eizan@chromium.org>
Acked-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240202141109.1.I24277520ac754ea538c9b14578edc94e1df11b48@changeid
Copy intel_dp_max_data_rate() to DRM core. It will be needed by a
follow-up DP tunnel patch, checking the maximum rate the DPRX (sink)
supports. Accordingly use the drm_dp_max_dprx_data_rate() name for
clarity. This patchset will also switch calling the new DRM function
in i915 instead of intel_dp_max_data_rate().
While at it simplify the function documentation/comments, removing
parts described already by drm_dp_bw_channel_coding_efficiency().
v2: (Ville)
- Remove max_link_rate_kbps.
- Simplify the function documentation.
v3:
- Rebased on latest drm-tip.
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240226185246.1276018-1-imre.deak@intel.com
Add helpers drivers can use to calculate the BW allocation overhead -
due to SSC, FEC, DSC and data alignment on symbol cycles - and the
channel coding efficiency - due to the 8b/10b, 128b/132b encoding. On
128b/132b links the FEC overhead is part of the coding efficiency, so
not accounted for in the BW allocation overhead.
The drivers can use these functions to calculate a ratio, controlling
the stream symbol insertion rate of the source device in each SST TU
or MST MTP frame. Drivers can calculate this
m/n = (pixel_data_rate * drm_dp_bw_overhead()) /
(link_data_rate * drm_dp_bw_channel_coding_efficiency())
ratio for a given link and pixel stream and with that the
slots_per_mtp = CEIL(64 * m / n)
allocated slots per MTP for the stream in a link frame and with
that the
pbn = slots_per_mtp * drm_mst_get_pbn_divider()
allocated PBNs for the stream on the MST link path.
Take drm_dp_bw_overhead() into use in drm_dp_calc_pbn_mode(), for
drivers calculating the PBN value directly.
v2:
- Add dockbook description to drm_dp_bw_channel_coding_efficiency().
(LKP).
- Clarify the way m/n ratio is calculated in the commit log.
v3:
- Fix compile breakage for !CONFIG_BACKLIGHT_CLASS_DEVICE. (LKP)
- Account for FEC_PM overhead (+ 0.0015625 %), add comment
with the formula to calculate the total FEC overhead. (Ville)
v4:
- Rename DRM_DP_OVERHEAD_SSC to DRM_DP_OVERHEAD_SSC_REF_CLK. (Ville)
v5:
- Clarify in the commit log what MTP means.
- Simplify the commit log's formula to calculate PBN.
Cc: Lyude Paul <lyude@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: kernel test robot <lkp@intel.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> (v2)
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231107001505.3370108-1-imre.deak@intel.com
When doing DP AUX transfers there are two actors that need to be
powered in order for the DP AUX transfer to work: the DP source and
the DP sink. Commit bacbab58f0 ("drm: Mention the power state
requirement on side-channel operations") added some documentation
saying that the DP source is required to power itself up (if needed)
to do AUX transfers. However, that commit doesn't talk anything about
the DP sink.
For full fledged DP the sink isn't really a problem. It's expected
that if an external DP monitor isn't plugged in that attempting to do
AUX transfers won't work. It's also expected that if a DP monitor is
plugged in (and thus asserting HPD) then AUX transfers will work.
When we're looking at eDP, however, things are less obvious. Let's add
some documentation about expectations. Here's what we'll say:
1. We don't expect the DP AUX transfer function to power on an eDP
panel. If an eDP panel is physically connected but powered off then it
makes sense for the transfer to fail.
2. We'll document that the official way to power on a panel is via the
bridge chain, specifically by making sure that the panel's prepare
function has been called (which is called by
panel_bridge_pre_enable()). It's already specified in the kernel doc
of drm_panel_prepare() that this is the way to power the panel on and
also that after this call "it is possible to communicate with any
integrated circuitry via a command bus."
3. We'll also document that for code running in the panel driver
itself that it is legal for the panel driver to power itself up
however it wants (it doesn't need to officially call
drm_panel_pre_enable()) and then it can do AUX bus transfers. This is
currently the way that edp-panel works when it's running atop the DP
AUX bus.
NOTE: there was much discussion of all of this in response to v1 [1]
of this patch. A summary of that is:
* With the Intel i195 driver, apparently eDP panels do get powered
up. We won't forbid this but it is expected that code that wants to
run on a variety of platforms should ensure that the drm_panel's
prepare() function has been called.
* There is at least a reasonable amount of agreement that the
transfer() functions itself shouldn't be responsible for powering
the panel. It's proposed that if we need the DP AUX dev nodes to be
robust for eDP that the code handling the DP AUX dev nodes could
handle powering the panel by ensuring that the panel's prepare()
call was made. Potentially drm_dp_aux_dev_get_by_minor() could be a
good place to do this. This is left as a future exercise. Until
that's fixed the DP AUX dev nodes for eDP are probably best just
used for debugging.
* If a panel could be in PSR and DP AUX via the dev node needs to be
reliable then we need to be able to pull the panel out of PSR. On
i915 this is also apparently handled as part of the transfer()
function.
[1] https://lore.kernel.org/r/20220503162033.1.Ia8651894026707e4fa61267da944ff739610d180@changeid
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220509161733.v2.1.Ia8651894026707e4fa61267da944ff739610d180@changeid
Rename dp/ to display/ to account for additional display-related
helpers, such as HDMI. Update all related include statements. No
functional changes.
Various drivers, such as i915 and amdgpu, use similar naming scheme
by putting code for video-output standards into a local display/
directory. The new directory's name is aligned with this convention.
v2:
* update commit message (Javier)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220421073108.19226-3-tzimmermann@suse.de
