[PATCH v3 1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook

[PATCH v3 1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook

[Imre Deak]

Prevent accessing the HW from the SDVO/TV get_modes connector hook.
Returning 0 from the hook will make the caller -
drm_helper_probe_single_connector_modes() - return a default/EDID
override mode list to users. This matches the case where
intel_sdvo_get_tv_modes() fails to retrieve the current mode list due to
a HW access failure.

v2: Clarify the commit message wrt. which modes get_modes() returns. (Jouni)

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240208111838.1950411-1-imre.deak@intel.com
---
 drivers/gpu/drm/i915/display/intel_sdvo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_sdvo.c b/drivers/gpu/drm/i915/display/intel_sdvo.c
index 412c15d32f07e..c67605059aa3e 100644
--- a/drivers/gpu/drm/i915/display/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/display/intel_sdvo.c
@@ -2312,6 +2312,9 @@ static int intel_sdvo_get_tv_modes(struct drm_connector *connector)
 	drm_dbg_kms(&i915->drm, "[CONNECTOR:%d:%s]\n",
 		    connector->base.id, connector->name);
 
+	if (!intel_display_driver_check_access(i915))
+		return 0;
+
 	/*
 	 * Read the list of supported input resolutions for the selected TV
 	 * format.
-- 
2.39.2

[PATCH v3 2/2] drm/i915: Prevent HW access during init from connector get_modes hooks

[Imre Deak]

Prevent accessing the HW from the get_modes hooks of connectors deriving
the mode list from the display's EDID. drm_edid_connector_add_modes()
will return the mode list based on the EDID which was cached during a
previous detection/get_modes call.

This also fixes the NULL deref problem (10085) which was
introduced/revealed by

commit bab87ef4db9a ("drm/i915: Disable hotplug detection handlers during driver init/shutdown")

After the above change MST connectors will not change state during
driver init/shutdown; thus some of these connectors with no I2C/DDC
adapter registered for them (since the given MST port has no sink
connected) may stay then in the 'unknown' connector status. The
get_modes() hook should not try to use the I2C/DDC adapter in this state
(which would lead to the above NULL deref) which this patch ensures.

v2:
- Remove the redundant check from intel_crt_ddc_get_modes().
- Rebase on latest drm-tip.
- Add Fixes: line / related commit notes.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10085
Fixes: bab87ef4db9a ("drm/i915: Disable hotplug detection handlers during driver init/shutdown")
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240206153910.1758057-3-imre.deak@intel.com
---
 drivers/gpu/drm/i915/display/intel_crt.c    | 3 +++
 drivers/gpu/drm/i915/display/intel_dp_mst.c | 4 ++++
 drivers/gpu/drm/i915/display/intel_dvo.c    | 5 +++++
 drivers/gpu/drm/i915/display/intel_sdvo.c   | 4 ++++
 4 files changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_crt.c b/drivers/gpu/drm/i915/display/intel_crt.c
index b9733a73e21d4..93479db0f89f6 100644
--- a/drivers/gpu/drm/i915/display/intel_crt.c
+++ b/drivers/gpu/drm/i915/display/intel_crt.c
@@ -933,6 +933,9 @@ static int intel_crt_get_modes(struct drm_connector *connector)
 	struct i2c_adapter *ddc;
 	int ret;
 
+	if (!intel_display_driver_check_access(dev_priv))
+		return drm_edid_connector_add_modes(connector);
+
 	wakeref = intel_display_power_get(dev_priv,
 					  intel_encoder->power_domain);
 
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 5fa25a5a36b55..5307ddd4edcf5 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -1197,6 +1197,7 @@ static bool intel_dp_mst_initial_fastset_check(struct intel_encoder *encoder,
 static int intel_dp_mst_get_ddc_modes(struct drm_connector *connector)
 {
 	struct intel_connector *intel_connector = to_intel_connector(connector);
+	struct drm_i915_private *i915 = to_i915(intel_connector->base.dev);
 	struct intel_dp *intel_dp = intel_connector->mst_port;
 	const struct drm_edid *drm_edid;
 	int ret;
@@ -1204,6 +1205,9 @@ static int intel_dp_mst_get_ddc_modes(struct drm_connector *connector)
 	if (drm_connector_is_unregistered(connector))
 		return intel_connector_update_modes(connector, NULL);
 
+	if (!intel_display_driver_check_access(i915))
+		return drm_edid_connector_add_modes(connector);
+
 	drm_edid = drm_dp_mst_edid_read(connector, &intel_dp->mst_mgr, intel_connector->port);
 
 	ret = intel_connector_update_modes(connector, drm_edid);
diff --git a/drivers/gpu/drm/i915/display/intel_dvo.c b/drivers/gpu/drm/i915/display/intel_dvo.c
index 8ca9ae4798a89..c076da75b066e 100644
--- a/drivers/gpu/drm/i915/display/intel_dvo.c
+++ b/drivers/gpu/drm/i915/display/intel_dvo.c
@@ -30,6 +30,7 @@
 
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_crtc.h>
+#include <drm/drm_edid.h>
 
 #include "i915_drv.h"
 #include "i915_reg.h"
@@ -338,8 +339,12 @@ intel_dvo_detect(struct drm_connector *_connector, bool force)
 static int intel_dvo_get_modes(struct drm_connector *_connector)
 {
 	struct intel_connector *connector = to_intel_connector(_connector);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
 	int num_modes;
 
+	if (!intel_display_driver_check_access(i915))
+		return drm_edid_connector_add_modes(&connector->base);
+
 	/*
 	 * We should probably have an i2c driver get_modes function for those
 	 * devices which will have a fixed set of modes determined by the chip
diff --git a/drivers/gpu/drm/i915/display/intel_sdvo.c b/drivers/gpu/drm/i915/display/intel_sdvo.c
index c67605059aa3e..825638702ac1b 100644
--- a/drivers/gpu/drm/i915/display/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/display/intel_sdvo.c
@@ -2202,12 +2202,16 @@ intel_sdvo_detect(struct drm_connector *connector, bool force)
 
 static int intel_sdvo_get_ddc_modes(struct drm_connector *connector)
 {
+	struct drm_i915_private *i915 = to_i915(connector->dev);
 	int num_modes = 0;
 	const struct drm_edid *drm_edid;
 
 	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s]\n",
 		    connector->base.id, connector->name);
 
+	if (!intel_display_driver_check_access(i915))
+		return drm_edid_connector_add_modes(connector);
+
 	/* set the bus switch and get the modes */
 	drm_edid = intel_sdvo_get_edid(connector);
 
-- 
2.39.2

✗ Fi.CI.BUILD: failure for series starting with [v3,1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook

[Patchwork]

== Series Details ==

Series: series starting with [v3,1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook
URL   : https://patchwork.freedesktop.org/series/129727/
State : failure

== Summary ==

Error: make failed
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  CC [M]  drivers/gpu/drm/i915/display/intel_sdvo.o
drivers/gpu/drm/i915/display/intel_sdvo.c: In function ‘intel_sdvo_get_tv_modes’:
drivers/gpu/drm/i915/display/intel_sdvo.c:2305:41: error: ‘i915’ undeclared (first use in this function); did you mean ‘I915’?
 2305 |  if (!intel_display_driver_check_access(i915))
      |                                         ^~~~
      |                                         I915
drivers/gpu/drm/i915/display/intel_sdvo.c:2305:41: note: each undeclared identifier is reported only once for each function it appears in
make[6]: *** [scripts/Makefile.build:243: drivers/gpu/drm/i915/display/intel_sdvo.o] Error 1
make[5]: *** [scripts/Makefile.build:481: drivers/gpu/drm/i915] Error 2
make[4]: *** [scripts/Makefile.build:481: drivers/gpu/drm] Error 2
make[3]: *** [scripts/Makefile.build:481: drivers/gpu] Error 2
make[2]: *** [scripts/Makefile.build:481: drivers] Error 2
make[1]: *** [/home/kbuild2/kernel/Makefile:1921: .] Error 2
make: *** [Makefile:240: __sub-make] Error 2
Build failed, no error log produced

Re: ✗ Fi.CI.BUILD: failure for series starting with [v3,1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook

[Imre Deak]

On Fri, Feb 09, 2024 at 05:23:08PM +0000, Patchwork wrote:
> == Series Details ==
> 
> Series: series starting with [v3,1/2] drm/i915: Prevent HW access during init from SDVO TV get_modes hook
> URL   : https://patchwork.freedesktop.org/series/129727/
> State : failure
> 
> == Summary ==
> 
> Error: make failed
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   INSTALL libsubcmd_headers
>   CC [M]  drivers/gpu/drm/i915/display/intel_sdvo.o
> drivers/gpu/drm/i915/display/intel_sdvo.c: In function ‘intel_sdvo_get_tv_modes’:
> drivers/gpu/drm/i915/display/intel_sdvo.c:2305:41: error: ‘i915’ undeclared (first use in this function); did you mean ‘I915’?
>  2305 |  if (!intel_display_driver_check_access(i915))
>       |                                         ^~~~
>       |                                         I915
> drivers/gpu/drm/i915/display/intel_sdvo.c:2305:41: note: each undeclared identifier is reported only once for each function it appears in
> make[6]: *** [scripts/Makefile.build:243: drivers/gpu/drm/i915/display/intel_sdvo.o] Error 1
> make[5]: *** [scripts/Makefile.build:481: drivers/gpu/drm/i915] Error 2
> make[4]: *** [scripts/Makefile.build:481: drivers/gpu/drm] Error 2
> make[3]: *** [scripts/Makefile.build:481: drivers/gpu] Error 2
> make[2]: *** [scripts/Makefile.build:481: drivers] Error 2
> make[1]: *** [/home/kbuild2/kernel/Makefile:1921: .] Error 2
> make: *** [Makefile:240: __sub-make] Error 2
> Build failed, no error log produced

Not sure why this fails, on latest drm-tip I get a different result, see
below.

Looks like an old tree is used as the base, could someone from the CI
team check this?

$ git fetch drm-tip
$ git reset --hard drm-tip/drm-tip
HEAD is now at 2aceb3c0b9c8c drm-tip: 2024y-02m-09d-12h-48m-25s UTC integration manifest
$ git am ~/imre.mbox
Applying: drm/i915: Prevent HW access during init from SDVO TV get_modes hook
Applying: drm/i915: Prevent HW access during init from connector get_modes hooks
$ make
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  CC [M]  drivers/gpu/drm/i915/display/intel_crt.o
  CC [M]  drivers/gpu/drm/i915/display/intel_dp_mst.o
  CC [M]  drivers/gpu/drm/i915/display/intel_dvo.o
  CC [M]  drivers/gpu/drm/i915/display/intel_sdvo.o
  LD [M]  drivers/gpu/drm/i915/i915.o
  CC [M]  drivers/gpu/drm/xe/i915-display/intel_dp_mst.o
  LD [M]  drivers/gpu/drm/xe/xe.o
  MODPOST Module.symvers
Kernel: arch/x86/boot/bzImage is ready  (#1476)
  LD [M]  drivers/gpu/drm/i915/i915.ko
  LD [M]  drivers/gpu/drm/xe/xe.ko