On 5/17/21 3:32 AM, Jan Beulich wrote:

On 14.05.2021 02:56, Connor Davis wrote:

quoted

Check if the debug capability is enabled in early_xdbc_parse_parameter,
and if it is, return with an error. This avoids collisions with whatever
enabled the DbC prior to linux starting.

Doesn't this go too far and prevent use even if firmware (perhaps
mistakenly) left it enabled?

Jan

Yes, but how is one supposed to distinguish the broken firmware and 
non-broken

firmware cases?

quoted

Signed-off-by: Connor Davis <redacted>
---
  drivers/usb/early/xhci-dbc.c | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index be4ecbabdd58..ca67fddc2d36 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c

@@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s)
  	}
  	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
  
+	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
+		pr_notice("xhci debug capability already in use\n");
+		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+		xdbc.xdbc_reg = NULL;
+		xdbc.xhci_base = NULL;
+		xdbc.xhci_length = 0;
+
+		return -ENODEV;
+	}
+
  	return 0;
  }
  

Thanks,

Connor