From b74218f2aeeda3f7ec18a54c9f2e6bee9a4a6c94 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Povi=C5=A1er?= <povik@cutebit.org>
Date: Wed, 22 Feb 2023 15:24:21 +0100
Subject: [PATCH] display: Factor out top of memory allocation
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Move it into utils.c before we reuse it for SIO data.

Signed-off-by: Martin Povišer <povik@cutebit.org>
---
 src/display.c |  7 +------
 src/utils.c   | 20 ++++++++++++++++++++
 src/utils.h   |  1 +
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/display.c b/src/display.c
index 3dbf49ea..21bf41f3 100644
--- a/src/display.c
+++ b/src/display.c
@@ -369,12 +369,7 @@ int display_configure(const char *config)
             return -1;
         }
 
-        cur_boot_args.mem_size -= size;
-        fb_pa = cur_boot_args.phys_base + cur_boot_args.mem_size;
-        /* add guard page between RAM and framebuffer */
-        // TODO: update mapping?
-        cur_boot_args.mem_size -= SZ_16K;
-
+        fb_pa = top_of_memory_alloc(size);
         memset((void *)fb_pa, 0, size);
 
         tmp_dva = iova_alloc(dcp->iovad_dcp, size);
diff --git a/src/utils.c b/src/utils.c
index 23434762..ff8dd84b 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -180,3 +180,23 @@ bool is_heap(void *addr)
 
     return p > top_of_kernel_data && p < top_of_ram;
 }
+
+// TODO: update mapping?
+u64 top_of_memory_alloc(size_t size)
+{
+    static bool guard_page_inserted = false;
+    cur_boot_args.mem_size -= ALIGN_UP(size, SZ_16K);
+    u64 ret = cur_boot_args.phys_base + cur_boot_args.mem_size;
+
+    if (!guard_page_inserted) {
+        cur_boot_args.mem_size -= SZ_16K;
+        guard_page_inserted = true;
+    } else {
+        // If the guard page was already there, move it down and allocate
+        // above it -- this is accomplished by simply shifting the allocated
+        // region by one page up.
+        ret += SZ_16K;
+    }
+
+    return ret;
+}
diff --git a/src/utils.h b/src/utils.h
index 1d053d2e..0e76221d 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -440,5 +440,6 @@ extern struct vector_args next_stage;
 void deep_wfi(void);
 
 bool is_heap(void *addr);
+u64 top_of_memory_alloc(size_t size);
 
 #endif