From cd41ed1758f4842d7b78870385e16b579cc89c38 Mon Sep 17 00:00:00 2001
From: Kimplul <kimi.h.kuparinen@gmail.com>
Date: Sun, 25 Jan 2026 17:14:53 +0200
Subject: implement dmem semi-properly

+ Add tests and fix virtual mapping, this is enough to start writing
  proper userspace drivers
---
 src/dmem.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 58 insertions(+), 19 deletions(-)

(limited to 'src/dmem.c')

diff --git a/src/dmem.c b/src/dmem.c
index d21a9c5..6b98003 100644
--- a/src/dmem.c
+++ b/src/dmem.c
@@ -19,13 +19,8 @@ static struct mem_region_root post_ram = { 0 };
 
 stat_t init_devmem(pm_t ram_base, pm_t ram_top)
 {
-	size_t pre_pages = __pages(ram_base);
-	size_t ram_pages = __pages(ram_top - ram_base);
-	/* -1 being the effective highest address possible */
-	size_t post_pages = __pages(-1) - ram_pages - pre_pages;
-
-	init_region(&pre_ram, 0, pre_pages, 0);
-	init_region(&post_ram, ram_top, post_pages, 0);
+	init_region(&pre_ram, 0, ram_base, 0);
+	init_region(&post_ram, ram_top, -1, 0);
 	return OK;
 }
 
@@ -54,39 +49,83 @@ vm_t alloc_devmem(struct tcb *t, pm_t start, size_t bytes, vmflags_t flags)
 	if (!region)
 		return NULL;
 
-	vm_t v = alloc_region(region, bytes, &bytes, flags);
-	if (!v)
+	/* carve out physical region (vm_t is misleading, this region is
+	 * physical memory) */
+	vm_t p = alloc_fixed_region(region, start, bytes, &bytes, flags);
+	if (!p)
+		return NULL;
+
+	/* carve out virtual region */
+	vm_t v = alloc_region(&t->uvmem.region, bytes, &bytes, flags | MR_DEV);
+	if (!v) {
+		free_region(region, p);
 		return NULL;
+	}
 
-	if (map_fixed_region(t->proc.vmem, v, start, bytes, flags)) {
+	/* convert from literal physical address to direct mapping address,
+	 * which map_* expects (kind of annoying to deal with, admittedly, is
+	 * there maybe a better way to handle these things?) */
+	p = (pm_t)__va(p);
+	if (map_fixed_region(t->proc.vmem, v, p, bytes, flags)) {
 		unmap_region(t->proc.vmem, v, bytes);
-		free_region(region, v);
+		free_region(&t->uvmem.region, v);
+		free_region(region, p);
 		return NULL;
 	}
 
 	return v;
 }
 
-stat_t free_devmem(struct tcb *t, vm_t start)
+stat_t free_known_devmem(struct tcb *t, struct mem_region *m)
 {
 	assert(t && is_proc(t));
+
+	/* ensure region is a device memory region and is currently not shared */
+	assert(is_set(m->flags, MR_DEV));
+	assert(m->pid != 0 || m->refcount == 1);
+
 	pm_t addr = 0;
-	stat_vpage(t->proc.vmem, start, &addr, NULL, NULL);
+	stat_vpage(t->proc.vmem, __addr(m->start), &addr, NULL, NULL);
 
-	struct mem_region_root *region = __select_region((pm_t)__pa(addr));
+	/* free physical device memory */
+	pm_t p = (pm_t)__pa(addr);
+	struct mem_region_root *region = __select_region(p);
 	if (!region)
 		return ERR_INVAL;
 
+	free_region(region, p);
 
-	struct mem_region *m = find_used_region(region, start);
-	if (!m)
-		return ERR_NF;
-
+	/* free virtual allocation associated with device mem */
 	vm_t base = __addr(m->start);
 	vm_t end = __addr(m->end);
+
+	/* free virtual memory associated with physical mapping */
 	size_t size = end - base;
 	unmap_fixed_region(t->proc.vmem, base, size);
 
-	free_region(region, base);
+	free_known_region(&t->uvmem.region, m);
+	return OK;
+}
+
+stat_t free_devmem(struct tcb *t, vm_t start)
+{
+	assert(t && is_proc(t));
+	struct mem_region *m = find_used_region(&t->uvmem.region, start);
+	if (!m)
+		return ERR_NF;
+
+	/* not a devmem region */
+	if (!is_set(m->flags, MR_DEV))
+		return ERR_INVAL;
+
+	/* mapping is shared, can't free right now */
+	if (m->pid == 0 && m->refcount > 1)
+		return ERR_INVAL;
+
+	stat_t ret = free_known_devmem(t, m);
+	if (ret)
+		return ret;
+
+	free_known_region(&t->uvmem.region, m);
 	return OK;
 }
-- 
cgit v1.3