The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Thanks, Sasha
------------------ original commit in Linus's tree ------------------
From 7af03e688792293ba33149fb8df619a8dff90e80 Mon Sep 17 00:00:00 2001 From: Jani Nikula jani.nikula@intel.com Date: Fri, 8 Mar 2024 18:03:39 +0200 Subject: [PATCH] drm/probe-helper: warn about negative .get_modes()
The .get_modes() callback is supposed to return the number of modes, never a negative error code. If a negative value is returned, it'll just be interpreted as a negative count, and added to previous calculations.
Document the rules, but handle the negative values gracefully with an error message.
Cc: stable@vger.kernel.org Acked-by: Thomas Zimmermann tzimmermann@suse.de Link: https://patchwork.freedesktop.org/patch/msgid/50208c866facc33226a3c77b82bb96... Signed-off-by: Jani Nikula jani.nikula@intel.com --- drivers/gpu/drm/drm_probe_helper.c | 7 +++++++ include/drm/drm_modeset_helper_vtables.h | 3 ++- 2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 19ecb749704be..75f84753f6ee3 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -422,6 +422,13 @@ static int drm_helper_probe_get_modes(struct drm_connector *connector)
count = connector_funcs->get_modes(connector);
+ /* The .get_modes() callback should not return negative values. */ + if (count < 0) { + drm_err(connector->dev, ".get_modes() returned %pe\n", + ERR_PTR(count)); + count = 0; + } + /* * Fallback for when DDC probe failed in drm_get_edid() and thus skipped * override/firmware EDID. diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h index 881b03e4dc288..9ed42469540eb 100644 --- a/include/drm/drm_modeset_helper_vtables.h +++ b/include/drm/drm_modeset_helper_vtables.h @@ -898,7 +898,8 @@ struct drm_connector_helper_funcs { * * RETURNS: * - * The number of modes added by calling drm_mode_probed_add(). + * The number of modes added by calling drm_mode_probed_add(). Return 0 + * on failures (no modes) instead of negative error codes. */ int (*get_modes)(struct drm_connector *connector);