Re: [PATCH] drm/vmwgfx: Filter modes which exceed 3/4 of graphics memory.

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Hi

Am 12.01.24 um 21:38 schrieb Ian Forbes:
SVGA requires surfaces to fit within graphics memory (max_mob_pages) which
means that modes with a final buffer size that would exceed graphics memory
must be pruned otherwise creation will fail.

Additionally, device commands which use multiple graphics resources must
have all their resources fit within graphics memory for the duration of the
command. Thus we need a small carve out of 1/4 of graphics memory to ensure
commands likes surface copies to the primary framebuffer for cursor
composition or damage clips can fit within graphics memory.

This fixes an issue where VMs with low graphics memory (< 64MiB) configured
with high resolution mode boot to a black screen because surface creation
fails.

That is a long-standing problem, which we have observed with other drivers as well. On low-memory devices, TTM doesn't play well. The real fix would be to export all modes that possibly fit and sort out the invalid configurations in atomic_check. It's just a lot more work.

Did you consider simply ignoring vmwgfx devices with less than 64 MiB of VRAM?


Signed-off-by: Ian Forbes <ian.forbes@xxxxxxxxxxxx>
---
  drivers/gpu/drm/vmwgfx/vmwgfx_kms.c | 20 ++++++++++++--------
  1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
index 28ff30e32fab..39d6d17fc488 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c
@@ -2854,12 +2854,12 @@ enum drm_mode_status vmw_connector_mode_valid(struct drm_connector *connector,
  	struct vmw_private *dev_priv = vmw_priv(dev);
  	u32 max_width = dev_priv->texture_max_width;
  	u32 max_height = dev_priv->texture_max_height;
-	u32 assumed_cpp = 4;
+	u32 assumed_cpp = dev_priv->assume_16bpp ? 2 : 4;
+	u32 pitch = mode->hdisplay * assumed_cpp;
+	u64 total = mode->vdisplay * pitch;
+	bool using_stdu = dev_priv->active_display_unit == vmw_du_screen_target;
- if (dev_priv->assume_16bpp)
-		assumed_cpp = 2;
-
-	if (dev_priv->active_display_unit == vmw_du_screen_target) {
+	if (using_stdu) {
  		max_width  = min(dev_priv->stdu_max_width,  max_width);
  		max_height = min(dev_priv->stdu_max_height, max_height);
  	}
@@ -2870,9 +2870,13 @@ enum drm_mode_status vmw_connector_mode_valid(struct drm_connector *connector,
  	if (max_height < mode->vdisplay)
  		return MODE_BAD_VVALUE;
- if (!vmw_kms_validate_mode_vram(dev_priv,
-			mode->hdisplay * assumed_cpp,
-			mode->vdisplay))
+	if (using_stdu &&
+		(total > (dev_priv->max_mob_pages * PAGE_SIZE * 3 / 4) ||

IDK the details of vmwgfx's memory management, but instead of this '3/4 test', wouldn't it be better to partition the VRAM via TTM and test against the partition sizes?

Best regards
Thomas

+		total > dev_priv->max_mob_size)) {
+		return MODE_MEM;
+	}
+
+	if (!vmw_kms_validate_mode_vram(dev_priv, pitch, mode->vdisplay))
  		return MODE_MEM;
return MODE_OK;

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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