Re: [PATCH v2] drm/gma500: replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi
From: Thomas Zimmermann
Date: Thu Sep 12 2024 - 07:08:18 EST
Hi
Am 12.09.24 um 11:30 schrieb Jani Nikula:
On Thu, 12 Sep 2024, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
Hi
Am 12.09.24 um 10:48 schrieb Jani Nikula:
On Thu, 12 Sep 2024, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
Hi
Am 11.09.24 um 20:06 schrieb Tejas Vipin:
Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi since
monitor HDMI information is available after EDID is parsed. Additionally
rewrite the code the code to have fewer indentation levels.
The problem is that the entire logic is outdated. The content
of cdv_hdmi_detect() should go into cdv_hdmi_get_modes(), the detect_ctx
callback should be set to drm_connector_helper_detect_from_ddc() and
cdv_hdmi_detect() should be deleted. The result is that ->detect_ctx
will detect the presence of a display and ->get_modes will update EDID
and other properties.
I guess I didn't get the memo on this one.
What's the problem with reading the EDID at detect? The subsequent
drm_edid_connector_add_modes() called from .get_modes() does not need to
read the EDID again.
With drm_connector_helper_detect_from_ddc() there is already a helper
for detection. It makes sense to use it. And if we continue to update
the properties in detect (instead of get_modes), what is the correct
connector_status on errors? Right now and with the patch applied, detect
returns status_disconnected on errors. But this isn't correct if there
actually is a display. By separating detect and get_modes cleanly, we
can detect the display reliably, but also handle errors better than we
currently do in gma500. Get_modes is already expected to update the EDID
property, [1] for detect it's not so clear AFAICT. I think that from a
design perspective, it makes sense to have a read-only function that
only detects the physical state of the connector and a read-write
function that updates the connector's properties. Best regards Thomas
[1]
https://elixir.bootlin.com/linux/v6.10.9/source/include/drm/drm_modeset_helper_vtables.h#L865
So what if you can probe DDC but can't actually read an EDID of any
kind? IMO that's a detect failure.
Not being able to read the EDID is not a failure IMHO. It's better to
report a detected display and only provide minimal support, than to
outright reject it. The display is essential for most users being able
to use the computer at all, so it's often better to display something at
lower quality than display nothing at all.
Or how about things like CEC attach? Seems natural to do it at
.detect(). Doing it at .get_modes() just seems wrong. However, it needs
the EDID for physical address.
I just don't think one size fits all here.
The good thing about the EDID probe helpers is that it only reads a
minimal amount of data, like a single byte or the EDID header, so
something like that. Many drivers poll the DDC every 10 seconds via
->detect. Which means that code running in ->detect possibly runs
concurrently to other DRM operations, such as page flips. Hence,
->detect can interfere with the driver's hot path. The call to
->get_modes usually only runs after the connector status changes to
connected, which rarely happens. It's also not time critical as no
modeset has happened yet.
And as everyone copies code from everyone else, we should establish best
practices that take such things into account. Even with drivers that
don't use connector polling, such as gma500, we should encourage devs to
do the right thing and move code out of ->detect.
Best regards
Thomas
BR,
Jani.
I think it should be fine to do incremental refactors like the patch at
hand (modulo some issues I mention below).
BR,
Jani.
Do you have a device for testing such a change?
Best regards
Thomas
Signed-off-by: Tejas Vipin <tejasvipin76@xxxxxxxxx>
---
Changes in v2:
- Use drm_edid instead of edid
Link to v1: https://lore.kernel.org/all/20240910051856.700210-1-tejasvipin76@xxxxxxxxx/
---
drivers/gpu/drm/gma500/cdv_intel_hdmi.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/gma500/cdv_intel_hdmi.c b/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
index 2d95e0471291..701f8bbd5f2b 100644
--- a/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
+++ b/drivers/gpu/drm/gma500/cdv_intel_hdmi.c
@@ -128,23 +128,25 @@ static enum drm_connector_status cdv_hdmi_detect(
{
struct gma_encoder *gma_encoder = gma_attached_encoder(connector);
struct mid_intel_hdmi_priv *hdmi_priv = gma_encoder->dev_priv;
- struct edid *edid = NULL;
+ const struct drm_edid *drm_edid;
+ int ret;
enum drm_connector_status status = connector_status_disconnected;
- edid = drm_get_edid(connector, connector->ddc);
+ drm_edid = drm_edid_read_ddc(connector, connector->ddc);
Just drm_edid_read() is enough when you're using connector->ddc.
+ ret = drm_edid_connector_update(connector, drm_edid);
hdmi_priv->has_hdmi_sink = false;
hdmi_priv->has_hdmi_audio = false;
- if (edid) {
- if (edid->input & DRM_EDID_INPUT_DIGITAL) {
- status = connector_status_connected;
- hdmi_priv->has_hdmi_sink =
- drm_detect_hdmi_monitor(edid);
- hdmi_priv->has_hdmi_audio =
- drm_detect_monitor_audio(edid);
- }
- kfree(edid);
+ if (ret)
This error path leaks the EDID.
+ return status;
+
+ if (drm_edid_is_digital(drm_edid)) {
+ status = connector_status_connected;
+ hdmi_priv->has_hdmi_sink = connector->display_info.is_hdmi;
+ hdmi_priv->has_hdmi_audio = connector->display_info.has_audio;
}
+ drm_edid_free(drm_edid);
+
return status;
}
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)