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
As per Displayport spec section 5.2.1.2 ("Video Timing Format") says
that all detachable sinks shall support 640x480 @60Hz as a fail safe
mode.
A DP compliance test expected us to utilize the above fact when all
modes it presented to the DP source were not achievable. It presented
only modes that would be achievable with more lanes and/or higher
speeds than we had available and expected that when we couldn't do
that then we'd fall back to 640x480 even though it didn't advertise
this size.
In order to pass the compliance test (and also support any users who
might fall into a similar situation with their display), we need to
add 640x480 into the list of modes. However, we don't want to add
640x480 all the time. Despite the fact that the DP spec says all sinks
_shall support_ 640x480, they're not guaranteed to support it
_well_. Continuing to read the spec you can see that the display is
not required to really treat 640x480 equal to all the other modes. It
doesn't need to scale or anything--just display the pixels somehow for
failsafe purposes. It should also be noted that it's not hard to find
a display hooked up via DisplayPort that _doesn't_ support 640x480 at
all. The HP ZR30w screen I'm sitting in front of has a native DP port
and doesn't work at 640x480. I also plugged in a tiny 800x480 HDMI
display via a DP to HDMI adapter and that screen definitely doesn't
support 640x480.
As a compromise solution, let's only add the 640x480 mode if:
* We're on DP.
* All other modes have been pruned.
This acknowledges that 640x480 might not be the best mode to use but,
since sinks are _supposed_ to support it, we will at least fall back
to it if there's nothing else.
Note that we _don't_ add higher resolution modes like 1024x768 in this
case. We only add those modes for a failed EDID read where we have no
idea what's going on. In the case where we've pruned all modes then
instead we only want 640x480 which is the only defined "Fail Safe"
resolution.
This patch originated in response to Kuogee Hsieh's patch [1].
[1] https://lore.kernel.org/r/1650671124-14030-1-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220511155749.v3.2.I4ac7f55aa446699f8c200a23c10463256f6f439f@changeid
Split up the connector's mode_valid helper into a simple-pipe and a
mode-config helper. The simple-pipe helper tests for display-size
limits while the mode-config helper tests for memory-bandwidth limits.
Also add the mgag200_ prefix to mga_vga_calculate_mode_bandwidth() and
comment on the function's purpose.
The memory-bandwidth tests assume that the display uses 4 bytes per
pixel. The first models of G200SE-A only had 1.75 MiB of VRAM, which
limits these devices to 640x480-32.
v2:
* note the memory constraints on early G200SE-A
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220516134343.6085-8-tzimmermann@suse.de
Test for a mode's memory requirements in the device-wide mode_valid
helper. For simplicify, always assume a 32-bit color format. While
some rejected modes would work with less colors, implementing this
is probably not worth the effort.
Also remove the memory-related test from the connector's mode_valid
helper. The test uses the bpp value that users can specify on the
kernel's command line. This value is unrelated and the test would
belong into atomic_check.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220516134343.6085-7-tzimmermann@suse.de
Initialization of the I2C adapter was allowed to fail. The mgag200
driver would have continued without DDC support. Had this happened in
practice, it would have led to segmentation faults in the connector
code. Resolve this problem by failing driver initialization on I2C-
related errors.
v2:
* initialize 'ret' before drm_err() (kernel test robot)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220516134343.6085-3-tzimmermann@suse.de
Add support for atomic update of gamma lut.
With this patch the "Night light" feature of gnome3
is working properly on mgag200.
v2:
- Add a default linear gamma function
- renamed functions with mgag200 prefix
- use format's 4cc code instead of bit depth
- use better interpolation for 16bits gamma
- remove legacy function mga_crtc_load_lut()
- can't remove the call to drm_mode_crtc_set_gamma_size()
because it doesn't work with userspace.
- other small refactors
v3:
- change mgag200_crtc_set_gamma*() argument
to struct drm_format_info *format
- fix printk format to %p4cc for 4cc and %zu for size_t
- rebased to drm-misc-next.
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220513084900.1832381-1-jfalempe@redhat.com
Don't add a mode for the kernel's command-line parameters from
within the DRM client code. Doing so can result in an unusable
display. If there's no compatible command-line mode, the client
will use one of the connector's preferred modes.
All mode creation and validation has to be performed by the
connector. When clients run, the connector's fill_modes callback
has already processed the kernel parameters and validated each
mode before adding it. The connector's mode list does not contain
invalid modes.
v2:
* grammar in commit message (Javier)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220511183125.14294-4-tzimmermann@suse.de
