[PATCH 4/8] amdgpu: limit maximum BAR0 size when attempting to enlarge (v2)

[Darren Salt]

This is coarse, applying to all dGPUs.

v2: If there are no advertised sizes small enough, limit to the smallest
available.
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h        |  1 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 31 ++++++++++++++++++----
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    |  9 +++++++
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 327a0daf4a1d..c0e3e402023e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -194,6 +194,7 @@ static const bool debug_evictions; /* = false */
 
 extern int amdgpu_tmz;
 extern int amdgpu_reset_method;
+extern int amdgpu_max_bar_size;
 
 #ifdef CONFIG_DRM_AMDGPU_SI
 extern int amdgpu_si_support;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index b0f8ad603147..c6495a86b280 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -909,6 +909,7 @@ void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
 int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 {
 	int rbar_size, current_size;
+	int max_size = -1;
 	u64 current_bytes;
 	u32 available_sizes;
 	struct pci_bus *root;
@@ -924,13 +925,20 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 
 	current_bytes = pci_resource_len(adev->pdev, 0);
 
-	/* Skip if the BIOS has already enabled large BAR, covering the VRAM */
-	if (current_bytes >= adev->gmc.real_vram_size)
-		return 0;
-
 	current_size = current_bytes ? pci_rebar_bytes_to_size(current_bytes) : -1;
 	rbar_size = pci_rebar_bytes_to_size(adev->gmc.real_vram_size);
 
+	if (amdgpu_max_bar_size >= 0) {
+		max_size = max(amdgpu_max_bar_size, 8); /* clamp to min. 256MB */
+		/* Skip if the maximum size is the current size */
+		if (current_size == max_size)
+			return 0;
+		rbar_size = max_size;
+	}
+	else if (current_bytes >= adev->gmc.real_vram_size)
+		/* Skip if the BIOS has already enabled large BAR, covering the VRAM */
+		return 0;
+
 	/* Check if the root BUS has 64bit memory resources */
 	root = adev->pdev->bus;
 	while (root->parent)
@@ -947,6 +955,19 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 		return 0;
 
 	available_sizes = pci_rebar_get_possible_sizes(adev->pdev, 0);
+	if (max_size >= 0) {
+		/* Cause larger sizes to be ignored unless that would leave
+		 * no advertised sizes (which shouldn't happen).
+		 */
+		r = available_sizes & ~(-1 << (max_size + 1));
+		if (!r) {
+			/* No smaller sizes, so use the smallest advertised */
+			r = ffs(r);
+			if (r)
+				r = 1 << (r - 1);
+		}
+		available_sizes = r;
+	}
 	if (available_sizes == 0)
 		return 0;
 
@@ -971,7 +992,7 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 	pci_release_resource(adev->pdev, 0);
 
 	for (;
-	     rbar_size >= 0 && rbar_size > current_size;
+	     rbar_size >= 0;
 	     rbar_size = fls(available_sizes & ~(-1 << rbar_size)) - 1
 	    ) {
 		r = pci_resize_resource(adev->pdev, 0, rbar_size);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 06a5b6ae1c43..74baa8dafa5f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -150,6 +150,7 @@ int amdgpu_noretry;
 int amdgpu_force_asic_type = -1;
 int amdgpu_tmz = 0;
 int amdgpu_reset_method = -1; /* auto */
+int amdgpu_max_bar_size = -1;
 
 struct amdgpu_mgpu_info mgpu_info = {
 	.mutex = __MUTEX_INITIALIZER(mgpu_info.mutex),
@@ -765,6 +766,14 @@ module_param_named(tmz, amdgpu_tmz, int, 0444);
 MODULE_PARM_DESC(reset_method, "GPU reset method (-1 = auto (default), 0 = legacy, 1 = mode0, 2 = mode1, 3 = mode2, 4 = baco)");
 module_param_named(reset_method, amdgpu_reset_method, int, 0444);
 
+/**
+ * DOC: max_bar_size (int)
+ * The maximum BAR size, in megabytes. Only affects BARs which the BIOS hasn't already made larger.
+ * Unlimited by default.
+ */
+module_param_named(max_bar_size, amdgpu_max_bar_size, int, 0444);
+MODULE_PARM_DESC(max_bar_size, "Maximum FB BAR size, log2(megabytes) (default = -1, meaning unlimited; minimum is 8 for 256MB).");
+
 static const struct pci_device_id pciidlist[] = {
 #ifdef  CONFIG_DRM_AMDGPU_SI
 	{0x1002, 0x6780, PCI_ANY_ID, PCI_ANY_ID, 0, 0, CHIP_TAHITI},
-- 
2.20.1