[PATCH 5/7] amdgpu: limit maximum FB BAR size when attempting to enlarge

[Darren Salt]

This is coarse, applying to all dGPUs.
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h        | 1 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 8 +++++++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c    | 9 +++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 2efce7fa6a4b..c844e2a8500a 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -202,6 +202,7 @@ static const bool __maybe_unused no_system_mem_limit;
 extern int amdgpu_tmz;
 extern int amdgpu_reset_method;
 extern bool amdgpu_resize_bar;
+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 292796e9f83d..b6c5ee490cbf 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1125,7 +1125,13 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 	rbar_size = pci_rebar_bytes_to_size(adev->gmc.real_vram_size);
 	current_size = pci_rebar_get_current_size(adev->pdev, 0);
 
-	/* Skip if the BIOS has already enabled large BAR, covering the VRAM */
+	/* Skip if the BIOS has already enabled large BAR, covering the VRAM (or >= limit, if set) */
+	if (amdgpu_max_bar_size >= 0) {
+		const u32 max_size = max(amdgpu_max_bar_size, 8); /* clamp to min. 256MB */
+
+		if (rbar_size > max_size)
+			rbar_size = max_size;
+	}
 	if (current_size >= rbar_size)
 		return 0;
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 6df33df74775..0542843c7d63 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -162,6 +162,7 @@ int amdgpu_tmz;
 int amdgpu_reset_method = -1; /* auto */
 int amdgpu_num_kcq = -1;
 bool amdgpu_resize_bar = true;
+int amdgpu_max_bar_size = -1;
 
 struct amdgpu_mgpu_info mgpu_info = {
 	.mutex = __MUTEX_INITIALIZER(mgpu_info.mutex),
@@ -816,6 +817,14 @@ module_param_named(num_kcq, amdgpu_num_kcq, int, 0444);
 module_param_named(resize_bar, amdgpu_resize_bar, bool, 0444);
 MODULE_PARM_DESC(resize_bar, "Controls whether the FB BAR should be resized (default = true).");
 
+/**
+ * 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