# \[PATCH v45 2/7\] mailbox/pcc.c: ignore errors on type 4 channels.

- From: Adam Young \<hidden\>
- Date: 2026-07-21 17:53:15 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/07/17293256
- Thread: https://ratatoskr.run/netdev/2026/07/17293254/t.md

```text
THE ACPI spec states:

"[The Error status register] Contains the processor relative address,
represented in Generic Address Structure (GAS) format, of the Error status
register. This field is ignored by the OSPM on slave channels"

Referring to type 4 channels.

https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/14_Platform_Communications_Channel/Platform_Comm_Channel.html#hw-registers-based-communications-subspace-structure-type-5

Signed-off-by: Adam Young <redacted>
---
 drivers/mailbox/pcc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index da26578a8aab..3c059fe87ce4 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -270,6 +270,9 @@ static int pcc_mbox_error_check_and_clear(struct pcc_chan_info *pchan)
 	u64 val;
 	int ret;
 
+	if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_SLAVE_SUBSPACE)
+		return 0;
+
 	ret = pcc_chan_reg_read(&pchan->error, &val);
 	if (ret)
 		return ret;
-- 
2.43.0

```