linux-kernel - Re: [PATCH 03/14] mailbox: pcc: Drop unnecessary endianness conversion of pcc

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Message-ID: <5093286f-1db6-bab2-920d-71fe274ad251@huawei.com>
Date: Wed, 5 Mar 2025 12:02:13 +0800
From: "lihuisong (C)" <lihuisong@...wei.com>
To: Sudeep Holla <sudeep.holla@....com>, <linux-acpi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC: Jassi Brar <jassisinghbrar@...il.com>, Adam Young
	<admiyo@...amperecomputing.com>
Subject: Re: [PATCH 03/14] mailbox: pcc: Drop unnecessary endianness
 conversion of pcc_hdr.flags


在 2025/3/3 18:51, Sudeep Holla 写道:
> 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.
How to confirm ACPI works only on little-endian?
>
> 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.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>   drivers/mailbox/pcc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index 4c582fa2b8bf4c9a9368dba8220f567555dba963..c87a5b7fa6eaf7bcabe0d55f844961c499376938 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_ACK_FLAG_MASK)
It's recommanded to delete PCC_ACK_FLAG_MASK and use 
PCC_CMD_COMPLETION_NOTIFY.
They are from the same place, namely, 'Initiator Responder 
Communications Channel Flags'.
>   		pcc_send_data(chan, NULL);
>   	else
>   		pcc_chan_reg_read_modify_write(&pchan->cmd_update);
>