Hi
Am 02.09.26 um 10:45 schrieb Jani Nikula:
On Tue, 01 Sep 2026, Thomas Zimmermann <[email protected]> wrote:
Add drm_edid_detect_panel_size() to extract the panel's preferred
display resolution from a given EDID. Required for setting up DRM's
panel orientation quirks in sysfb drivers.
v3:
- mention use case in documentation (Jani)
- use is_detailed_timing_descriptor() (Jani)
- rename helper to drm_edid_detect_panel_size()
v2:
- handle EDID without pixel timing descriptor (Sashiko)
- fix checks for width and height pointers
Signed-off-by: Thomas Zimmermann <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
---
drivers/gpu/drm/drm_edid.c | 47 ++++++++++++++++++++++++++++++++++++++
include/drm/drm_edid.h | 2 ++
2 files changed, 49 insertions(+)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 9990a836d0b6..d5d9e77dc91b 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -7852,3 +7852,50 @@ bool drm_edid_is_digital(const struct drm_edid *drm_edid)
drm_edid->edid->input & DRM_EDID_INPUT_DIGITAL;
}
EXPORT_SYMBOL(drm_edid_is_digital);
+
+/**
+ * drm_edid_detect_panel_size - Get a panel's size from EDID
+ * @drm_edid: EDID of the panel.
+ * @width: Returns the panel's width in pixels per scanline, if given
+ * @height: Returns the panel's height in scanlines, if given
+ *
+ * This function detects the preferred size of a panel from the given
+ * EDID. There is no such information stored in the EDID block directly,
+ * but the preferred mode often corresponds to the panel's native geometry.
+ *
+ * This helper should only be used during initialization before the
+ * connector is available. For regular use, retrieve the available display
+ * modes with the connector functions.
+ *
+ * Return: Zero on success, or a negative errno code otherwise.
+ */
+int drm_edid_detect_panel_size(const struct drm_edid *drm_edid,
+ unsigned int *width, unsigned int *height)
+{
+ const struct edid *edid = drm_edid->edid;
+ const struct detailed_timing *dt;
+ const struct detailed_pixel_timing *pt;
+
+ /*
+ * Use display mode from the Preferred Timing Descriptor. For old
+ * and obscure displays, we might need better heuristics.
+ */
+
+ if (edid->revision < 4 && !(edid->features &
DRM_EDID_FEATURE_PREFERRED_TIMING))
+ return -EINVAL; /* no Preferred Timing Descriptor */
Okay, so I should've asked this n versions ago, but should that be
s/&&/||/ instead?
You're right. And I could have sworn that I took this logic from
somewhere in this file, but that doesn't seem to be the case. Apologies
for such a stupid mistake.
Best regards
Thomas
+
+ dt = &edid->detailed_timings[0];
+
+ if (!is_detailed_timing_descriptor(dt))
+ return -EINVAL;
+
+ pt = &dt->data.pixel_data;
+
+ if (width)
+ *width = (pt->hactive_hblank_hi & 0xf0) << 4 | pt->hactive_lo;
+ if (height)
+ *height = (pt->vactive_vblank_hi & 0xf0) << 4 | pt->vactive_lo;
+
+ return 0;
+}
+EXPORT_SYMBOL(drm_edid_detect_panel_size);
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 04f7a7f1f108..a2617aa34edf 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -490,5 +490,7 @@ u32 drm_edid_get_panel_id(const struct drm_edid *drm_edid);
bool drm_edid_match(const struct drm_edid *drm_edid,
const struct drm_edid_ident *ident);
bool drm_edid_has_quirk(struct drm_connector *connector, enum drm_edid_quirk
quirk);
+int drm_edid_detect_panel_size(const struct drm_edid *drm_edid,
+ unsigned int *width, unsigned int *height);
#endif /* __DRM_EDID_H__ */
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)
