linux-kernel - [PATCH v2 03/13] mailbox: pcc: Drop unnecessary endianness conversion of pcc

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Message-Id: <20250305-pcc_fixes_updates-v2-3-1b1822bc8746@arm.com>
Date: Wed, 05 Mar 2025 16:38:07 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Sudeep Holla <sudeep.holla@....com>, 
 Jassi Brar <jassisinghbrar@...il.com>, Huisong Li <lihuisong@...wei.com>, 
 Adam Young <admiyo@...amperecomputing.com>, 
 Robbie King <robbiek@...ghtlabs.com>
Subject: [PATCH v2 03/13] mailbox: pcc: Drop unnecessary endianness
 conversion of pcc_hdr.flags

The Sparse static checker flags a type mismatch warning related to
endianness conversion:

  |  warning: incorrect type in argument 1 (different base types)
  |     expected restricted __le32 const [usertype] *p
  |     got unsigned int *

This is because an explicit endianness conversion (le32_to_cpu()) was
applied unnecessarily to a pcc_hdr.flags field that is already in
little-endian format.

The PCC driver is only enabled on little-endian kernels due to its
dependency on ACPI and EFI, making the explicit conversion unnecessary.

The redundant conversion occurs in pcc_chan_check_and_ack() for the
pcc_hdr.flags field. Drop this unnecessary endianness conversion of
pcc_hdr.flags.

Also drop the redundant PCC_ACK_FLAG_MASK definition and use the
more appropriate and already defined PCC_CMD_COMPLETION_NOTIFY.

Signed-off-by: Sudeep Holla <sudeep.holla@....com>
---
 drivers/mailbox/pcc.c | 2 +-
 include/acpi/pcc.h    | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index 4c582fa2b8bf4c9a9368dba8220f567555dba963..42dd405482e407cf90e66917a46fb8e350e0eeaf 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -292,7 +292,7 @@ static void check_and_ack(struct pcc_chan_info *pchan, struct mbox_chan *chan)
 	 *
 	 * The PCC master subspace channel clears chan_in_use to free channel.
 	 */
-	if (le32_to_cpup(&pcc_hdr.flags) & PCC_ACK_FLAG_MASK)
+	if (pcc_hdr.flags & PCC_CMD_COMPLETION_NOTIFY)
 		pcc_send_data(chan, NULL);
 	else
 		pcc_chan_reg_read_modify_write(&pchan->cmd_update);
diff --git a/include/acpi/pcc.h b/include/acpi/pcc.h
index 699c1a37b8e7846362bae35477eb5736be15d79e..d1e506f041c5a80857d4a025fa3c1803746ba4b9 100644
--- a/include/acpi/pcc.h
+++ b/include/acpi/pcc.h
@@ -32,7 +32,6 @@ struct pcc_mbox_chan {
 #define PCC_CMD_COMPLETION_NOTIFY	BIT(0)
 
 #define MAX_PCC_SUBSPACES	256
-#define PCC_ACK_FLAG_MASK	0x1
 
 #ifdef CONFIG_PCC
 extern struct pcc_mbox_chan *

-- 
2.34.1