linux-kernel - Re: [PATCH] Staging: vt6655: Fix sparse warning. Restricted cast.

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Date: Tue, 9 Jan 2024 15:22:19 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: SilverPlate3 <arielsilver77@...il.com>
Cc: forest@...ttletooquiet.net, gregkh@...uxfoundation.org,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Staging: vt6655: Fix sparse warning. Restricted cast.

On Tue, Jan 09, 2024 at 09:27:04AM +0200, SilverPlate3 wrote:
> Running 'make M=drivers/staging/vt6655 C=2'
> causes sparse to generate few warnings.
> This patch fixes the following warnings by ensuring le64_to_cpu
> handles only __le64 values, thus dismissing chances of bad endianness.
> * drivers/staging/vt6655/card.c:302:45: warning: cast to restricted __le64
> * drivers/staging/vt6655/card.c:336:23: warning: cast to restricted __le64
> * drivers/staging/vt6655/card.c:804:23: warning: cast to restricted __le64
> * drivers/staging/vt6655/card.c:831:18: warning: cast to restricted __le64
> 
> Signed-off-by: Ariel Silver <arielsilver77@...il.com>
> ---
>  drivers/staging/vt6655/card.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/vt6655/card.c b/drivers/staging/vt6655/card.c
> index 350ab8f3778a..5dc2200466b7 100644
> --- a/drivers/staging/vt6655/card.c
> +++ b/drivers/staging/vt6655/card.c
> @@ -292,6 +292,7 @@ bool card_update_tsf(struct vnt_private *priv, unsigned char rx_rate,
>  {
>  	u64 local_tsf;
>  	u64 qwTSFOffset = 0;
> +	__le64 le_qwTSFOffset = 0;
>  
>  	local_tsf = vt6655_get_current_tsf(priv);
>  
> @@ -299,7 +300,8 @@ bool card_update_tsf(struct vnt_private *priv, unsigned char rx_rate,
>  		qwTSFOffset = CARDqGetTSFOffset(rx_rate, qwBSSTimestamp,
>  						local_tsf);
>  		/* adjust TSF, HW's TSF add TSF Offset reg */
> -		qwTSFOffset =  le64_to_cpu(qwTSFOffset);
> +		le_qwTSFOffset = cpu_to_le64(qwTSFOffset);
> +		qwTSFOffset = le64_to_cpu(le_qwTSFOffset);


This isn't right at all.  You've just to convert it and then convert it
back.  (In other words do nothing but in a very complicated way).

This isn't a bug, it's just an issue of annotations.  The code is
re-using a single variable to hold both cpu and little endian data.  So
the way to write the annotations is to create two variables, one that's
cpu endian and one that's little endian.

regards,
dan carpenter