drm/nouveau/i2c: fix number of aux event slots

This was completely bogus before, using maximum DCB device index rather
than maximum AUX ID to size the buffer that stores event refcounts.

*Pretty* unlikely to have been an actual problem on most configurations,
that is, unless you've got one of the rare boards that have off-chip DP.

There, it'll likely crash.

Cc: stable@vger.kernel.org # 6.4+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230719044051.6975-1-skeggsb@gmail.com

Author: Ben Skeggs

drivers/gpu/drm/nouveau/include/nvkm/subdev/i2c.h

@@ -16,7 +16,7 @@ struct nvkm_i2c_bus {
 	const struct nvkm_i2c_bus_func *func;
 	struct nvkm_i2c_pad *pad;
 #define NVKM_I2C_BUS_CCB(n) /* 'n' is ccb index */                           (n)
-#define NVKM_I2C_BUS_EXT(n) /* 'n' is dcb external encoder type */ ((n) + 0x100)
+#define NVKM_I2C_BUS_EXT(n) /* 'n' is dcb external encoder type */  ((n) + 0x10)
 #define NVKM_I2C_BUS_PRI /* ccb primary comm. port */                        -1
 #define NVKM_I2C_BUS_SEC /* ccb secondary comm. port */                      -2
 	int id;
@@ -38,7 +38,7 @@ struct nvkm_i2c_aux {
 	const struct nvkm_i2c_aux_func *func;
 	struct nvkm_i2c_pad *pad;
 #define NVKM_I2C_AUX_CCB(n) /* 'n' is ccb index */                           (n)
-#define NVKM_I2C_AUX_EXT(n) /* 'n' is dcb external encoder type */ ((n) + 0x100)
+#define NVKM_I2C_AUX_EXT(n) /* 'n' is dcb external encoder type */  ((n) + 0x10)
 	int id;
 
 	struct mutex mutex;

drivers/gpu/drm/nouveau/nvkm/subdev/i2c/base.c

@@ -260,10 +260,11 @@ nvkm_i2c_new_(const struct nvkm_i2c_func *func, struct nvkm_device *device,
 {
 	struct nvkm_bios *bios = device->bios;
 	struct nvkm_i2c *i2c;
+	struct nvkm_i2c_aux *aux;
 	struct dcb_i2c_entry ccbE;
 	struct dcb_output dcbE;
 	u8 ver, hdr;
-	int ret, i;
+	int ret, i, ids;
 
 	if (!(i2c = *pi2c = kzalloc(sizeof(*i2c), GFP_KERNEL)))
 		return -ENOMEM;
@@ -406,5 +407,11 @@ nvkm_i2c_new_(const struct nvkm_i2c_func *func, struct nvkm_device *device,
 		}
 	}
 
-	return nvkm_event_init(&nvkm_i2c_intr_func, &i2c->subdev, 4, i, &i2c->event);
+	ids = 0;
+	list_for_each_entry(aux, &i2c->aux, head)
+		ids = max(ids, aux->id + 1);
+	if (!ids)
+		return 0;
+
+	return nvkm_event_init(&nvkm_i2c_intr_func, &i2c->subdev, 4, ids, &i2c->event);
 }