Hi Jani
On 5/6/2022 4:16 AM, Jani Nikula wrote:
On Thu, 05 May 2022, Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
Ville,
On Tue, Apr 26, 2022 at 1:21 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
If we're unable to read the EDID for a display because it's corrupt /
bogus / invalid then we'll add a set of standard modes for the
display. When userspace looks at these modes it doesn't really have a
good concept for which mode to pick and it'll likely pick the highest
resolution one by default. That's probably not ideal because the modes
were purely guesses on the part of the Linux kernel.
Let's instead set 640x480 as the "preferred" mode when we have no EDID.
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---
drivers/gpu/drm/drm_edid.c | 9 +++++++++
1 file changed, 9 insertions(+)
Someone suggested that you might have an opinion on this patch and
another one I posted recently [1]. Do you have any thoughts on it?
Just to be clear: I'm hoping to land _both_ this patch and [1]. If you
don't have an opinion, that's OK too.
[1] https://lore.kernel.org/r/20220426114627.2.I4ac7f55aa446699f8c200a23c10463256f6f439f@changeid
There are a number of drivers with combos:
drm_add_modes_noedid()
drm_set_preferred_mode()
which I think would be affected by the change. Perhaps you should just
call drm_set_preferred_mode() in your referenced patch?
So it seems like many drivers handle the !edid case within their
respective get_modes() call which probably is because they know the max
capability of their connector and because they know which mode should be
set as preferred. But at the same time, perhaps the code below which
handles the count == 0 case should be changed like below to make sure we
are within the max_width/height of the connector (to handle the first
condition)?
diff --git a/drivers/gpu/drm/drm_probe_helper.c
b/drivers/gpu/drm/drm_probe_helper.c
index 682359512996..6eb89d90777b 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -517,7 +517,8 @@ int drm_helper_probe_single_connector_modes(struct
drm_connector *connector,
if (count == 0 && (connector->status ==
connector_status_connected ||
connector->status == connector_status_unknown))
- count = drm_add_modes_noedid(connector, 1024, 768);
+ count = drm_add_modes_noedid(connector,
connector->dev->mode_config.max_width,
+ connector->dev->mode_config.max_height);
count += drm_helper_probe_add_cmdline_mode(connector);
if (count == 0)
goto prune;
Alternatively, perhaps drm_set_preferred_mode() should erase the
previous preferred mode(s) if it finds a matching new preferred mode.
But still yes, even if we change it like above perhaps for other non-DP
cases its still better to allow individual drivers to pick their
preferred modes.
If we call drm_set_preferred_mode() in the referenced patch, it will not
address the no EDID cases because the patch comes into picture when
there was a EDID with some modes but not with 640x480.
So i think the second proposal is a good one. It will cover existing
users of drm_set_preferred_mode() as typically its called after
drm_add_modes_noedid() which means the existing users want to "override"
their preferred mode.
BR,
Jani.
