[Mesa-dev] [PATCH] vulkan/wsi: Report the correct min/maxImageCount

[Jason Ekstrand]

>From the Vulkan spec 1.0.32 section 29.6 docs for vkAcquireNextImageKHR:

   "Let n be the total number of images in the swapchain, m be the value of
   VkSurfaceCapabilitiesKHR::minImageCount, and a be the number of
   presentable images that the application has currently acquired (i.e.
   images acquired with vkAcquireNextImageKHR, but not yet presented with
   vkQueuePresentKHR).  vkAcquireNextImageKHR can always succeed if a ≤ n -
   m at the time vkAcquireNextImageKHR is called. vkAcquireNextImageKHR
   should not be called if a > n - m with a timeout of UINT64_MAX; in such
   a case, vkAcquireNextImageKHR may block indefinitely."

With minImageCount == 2 (as it was previously, the client is allowed to
acquire all but one image withoutblocking.  If we really need 4 images for
mailbox mode + pageflipping, then we need to request a minimum of 4 images
up-front.  This is a bit unfortunate because it means we will always
consume 4 images.  In the future, we may be able to optimize this a bit by
waiting until the server starts to flip and returning OUT_OF_DATE to get
the client to re-allocate with more images or something like that.

Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
---
 src/vulkan/wsi/wsi_common_wayland.c | 25 ++++++++++---------------
 src/vulkan/wsi/wsi_common_x11.c     | 21 ++++++++++-----------
 2 files changed, 20 insertions(+), 26 deletions(-)

diff --git a/src/vulkan/wsi/wsi_common_wayland.c b/src/vulkan/wsi/wsi_common_wayland.c
index c6e138e..41c099f 100644
--- a/src/vulkan/wsi/wsi_common_wayland.c
+++ b/src/vulkan/wsi/wsi_common_wayland.c
@@ -41,8 +41,6 @@
    memcpy((dest), (src), (count) * sizeof(*(src))); \
 })
 
-#define MIN_NUM_IMAGES 2
-
 struct wsi_wayland;
 
 struct wsi_wl_display {
@@ -366,8 +364,16 @@ static VkResult
 wsi_wl_surface_get_capabilities(VkIcdSurfaceBase *surface,
                                 VkSurfaceCapabilitiesKHR* caps)
 {
-   caps->minImageCount = MIN_NUM_IMAGES;
-   caps->maxImageCount = 4;
+   /* For true mailbox mode, we need at least 4 images:
+    *  1) One to scan out from
+    *  2) One to have queued for scan-out
+    *  3) One to be currently held by the Wayland compositor
+    *  4) One to render to
+    */
+   caps->minImageCount = 4;
+   /* There is no real maximum */
+   caps->maxImageCount = 0;
+
    caps->currentExtent = (VkExtent2D) { -1, -1 };
    caps->minImageExtent = (VkExtent2D) { 1, 1 };
    caps->maxImageExtent = (VkExtent2D) { INT16_MAX, INT16_MAX };
@@ -685,17 +691,6 @@ wsi_wl_surface_create_swapchain(VkIcdSurfaceBase *icd_surface,
 
    int num_images = pCreateInfo->minImageCount;
 
-   assert(num_images >= MIN_NUM_IMAGES);
-
-   /* For true mailbox mode, we need at least 4 images:
-    *  1) One to scan out from
-    *  2) One to have queued for scan-out
-    *  3) One to be currently held by the Wayland compositor
-    *  4) One to render to
-    */
-   if (pCreateInfo->presentMode == VK_PRESENT_MODE_MAILBOX_KHR)
-      num_images = MAX2(num_images, 4);
-
    size_t size = sizeof(*chain) + num_images * sizeof(chain->images[0]);
    chain = vk_alloc(pAllocator, size, 8,
                       VK_SYSTEM_ALLOCATION_SCOPE_OBJECT);
diff --git a/src/vulkan/wsi/wsi_common_x11.c b/src/vulkan/wsi/wsi_common_x11.c
index d120313d..208d8d4 100644
--- a/src/vulkan/wsi/wsi_common_x11.c
+++ b/src/vulkan/wsi/wsi_common_x11.c
@@ -375,8 +375,16 @@ x11_surface_get_capabilities(VkIcdSurfaceBase *icd_surface,
                                       VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
    }
 
+   /* For true mailbox mode, we need at least 4 images:
+    *  1) One to scan out from
+    *  2) One to have queued for scan-out
+    *  3) One to be currently held by the Wayland compositor
+    *  4) One to render to
+    */
    caps->minImageCount = 2;
-   caps->maxImageCount = 4;
+   /* There is no real maximum */
+   caps->maxImageCount = 0;
+
    caps->supportedTransforms = VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR;
    caps->currentTransform = VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR;
    caps->maxImageArrayLayers = 1;
@@ -911,16 +919,7 @@ x11_surface_create_swapchain(VkIcdSurfaceBase *icd_surface,
 
    assert(pCreateInfo->sType == VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR);
 
-   int num_images = pCreateInfo->minImageCount;
-
-   /* For true mailbox mode, we need at least 4 images:
-    *  1) One to scan out from
-    *  2) One to have queued for scan-out
-    *  3) One to be currently held by the Wayland compositor
-    *  4) One to render to
-    */
-   if (pCreateInfo->presentMode == VK_PRESENT_MODE_MAILBOX_KHR)
-      num_images = MAX2(num_images, 4);
+   const unsigned num_images = pCreateInfo->minImageCount;
 
    size_t size = sizeof(*chain) + num_images * sizeof(chain->images[0]);
    chain = vk_alloc(pAllocator, size, 8,
-- 
2.5.0.400.gff86faf