mailbox: pcc: Set txdone_irq/txdone_poll based on PCCT flags

The PCC controller currently enables txdone via IRQ if the PCCT exposes
platform capability to generate command completion interrupt, but it
leaves txdone_poll unchanged. Make the behaviour explicit:

  - If ACPI_PCCT_DOORBELL is present, use txdone_irq and disable polling.
  - Otherwise, disable txdone_irq and fall back to txdone_poll.

Configure the PCC mailbox to use interrupt-based completion for PCC types
that signal completion via IRQ using TXDONE_BY_IRQ, and fall back to
polling for others using TXDONE_BY_POLL.

This ensures the PCC driver uses the appropriate completion mechanism
according to the PCCT table definition and makes the completion mode
unambiguous avoiding mixed signalling when the platform lacks a doorbell
flag set.

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Adam Young <admiyo@os.amperecomputing.com>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Author: sudeep-holla

drivers/mailbox/pcc.c

@@ -791,8 +791,13 @@ static int pcc_mbox_probe(struct platform_device *pdev)
 		(unsigned long) pcct_tbl + sizeof(struct acpi_table_pcct));
 
 	acpi_pcct_tbl = (struct acpi_table_pcct *) pcct_tbl;
-	if (acpi_pcct_tbl->flags & ACPI_PCCT_DOORBELL)
+	if (acpi_pcct_tbl->flags & ACPI_PCCT_DOORBELL) {
 		pcc_mbox_ctrl->txdone_irq = true;
+		pcc_mbox_ctrl->txdone_poll = false;
+	} else {
+		pcc_mbox_ctrl->txdone_irq = false;
+		pcc_mbox_ctrl->txdone_poll = true;
+	}
 
 	for (i = 0; i < count; i++) {
 		struct pcc_chan_info *pchan = chan_info + i;