Re: [PATCH v2 02/22] drm: Add valid clones check

[Jessica Zhang]

On 12/16/2024 6:47 AM, Maxime Ripard wrote:
On Fri, Dec 06, 2024 at 04:48:43PM -0800, Jessica Zhang wrote:
On 9/25/2024 12:23 AM, Maxime Ripard wrote:
On Tue, Sep 24, 2024 at 03:59:18PM GMT, Jessica Zhang wrote:
Check that all encoders attached to a given CRTC are valid
possible_clones of each other.

Signed-off-by: Jessica Zhang <quic_jessz...@quicinc.com>
---
   drivers/gpu/drm/drm_atomic_helper.c | 23 +++++++++++++++++++++++
   1 file changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index 43cdf39019a4..cc4001804fdc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -574,6 +574,25 @@ mode_valid(struct drm_atomic_state *state)
        return 0;
   }
+static int drm_atomic_check_valid_clones(struct drm_atomic_state *state,
+                                        struct drm_crtc *crtc)
+{
+       struct drm_encoder *drm_enc;
+       struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state,
+                                                                         crtc);
+
+       drm_for_each_encoder_mask(drm_enc, crtc->dev, crtc_state->encoder_mask) 
{
+               if ((crtc_state->encoder_mask & drm_enc->possible_clones) !=
+                   crtc_state->encoder_mask) {
+                       DRM_DEBUG("crtc%d failed valid clone check for mask 
0x%x\n",
+                                 crtc->base.id, crtc_state->encoder_mask);
+                       return -EINVAL;
+               }
+       }
+
+       return 0;
+}
+
   /**
    * drm_atomic_helper_check_modeset - validate state object for modeset 
changes
    * @dev: DRM device
@@ -745,6 +764,10 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
                ret = drm_atomic_add_affected_planes(state, crtc);
                if (ret != 0)
                        return ret;
+
+               ret = drm_atomic_check_valid_clones(state, crtc);
+               if (ret != 0)
+                       return ret;
        }

Pretty much the same comment, we should have kunit tests for this.

Hey Maxime,

I'm working on the kunit test for this and had a question on the design for
the unit test:

Since this is a static helper that returns a pretty common error code, how
would you recommend going about making sure that
`drm_atomic_check_valid_clones()` specifically is returning the error (and
not a different part of check_modeset) when testing the check_valid_clones()
failure path?

There's two ways to go about it. Either you can unit test it, prepare a
series of custom states and use
EXPORT_SYMBOL_FOR_TESTS_ONLY/EXPORT_SYMBOL_IF_KUNIT, or you can go the
integration test way and just test that drm_atomic_check is rejected for
unsafe combinations.

I guess I'd prefer the former, but the latter also makes sense and
eventually, it checks what we want: to make sure that we reject such a
state. What part of the code does or with what error code is less
important imo.

Thanks for confirming! The changes I made are based on the latter 
approach. Will post the changes later today if you have no objections on 
this

Thanks,

Jessica Zhang


Maxime