netdev - Re: [PATCH net 1/2] net: dsa: qca8k: fix regmap bulk read/write methods on big endian systems

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Message-ID: <ZRwxrixyhOT29C47@kernel.org>
Date: Tue, 3 Oct 2023 17:22:22 +0200
From: Simon Horman <horms@...nel.org>
To: Marek Behún <kabel@...nel.org>
Cc: Christian Marangi <ansuelsmth@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: dsa: qca8k: fix regmap bulk read/write
 methods on big endian systems

On Mon, Oct 02, 2023 at 12:46:11PM +0200, Marek Behún wrote:
> Commit c766e077d927 ("net: dsa: qca8k: convert to regmap read/write
> API") introduced bulk read/write methods to qca8k's regmap.
> 
> The regmap bulk read/write methods get the register address in a buffer
> passed as a void pointer parameter (the same buffer contains also the
> read/written values). The register address occupies only as many bytes
> as it requires at the beginning of this buffer. For example if the
> .reg_bits member in regmap_config is 16 (as is the case for this
> driver), the register address occupies only the first 2 bytes in this
> buffer, so it can be cast to u16.
> 
> But the original commit implementing these bulk read/write methods cast
> the buffer to u32:
>   u32 reg = *(u32 *)reg_buf & U16_MAX;
> taking the first 4 bytes. This works on little endian systems where the
> first 2 bytes of the buffer correnspond to the low 16-bits, but it

nit: correspond

> obviously cannot work on big endian systems.
> 
> Fix this by casting the beginning of the buffer to u16 as
>    u32 reg = *(u16 *)reg_buf;
> 
> Fixes: c766e077d927 ("net: dsa: qca8k: convert to regmap read/write API")
> Signed-off-by: Marek Behún <kabel@...nel.org>
> ---
>  drivers/net/dsa/qca/qca8k-8xxx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> index de1dc22cf683..d2df30640269 100644
> --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> @@ -505,8 +505,8 @@ qca8k_bulk_read(void *ctx, const void *reg_buf, size_t reg_len,
>  		void *val_buf, size_t val_len)
>  {
>  	int i, count = val_len / sizeof(u32), ret;
> -	u32 reg = *(u32 *)reg_buf & U16_MAX;
>  	struct qca8k_priv *priv = ctx;
> +	u32 reg = *(u16 *)reg_buf;
>  
>  	if (priv->mgmt_master &&
>  	    !qca8k_read_eth(priv, reg, val_buf, val_len))
> @@ -527,8 +527,8 @@ qca8k_bulk_gather_write(void *ctx, const void *reg_buf, size_t reg_len,
>  			const void *val_buf, size_t val_len)
>  {
>  	int i, count = val_len / sizeof(u32), ret;
> -	u32 reg = *(u32 *)reg_buf & U16_MAX;
>  	struct qca8k_priv *priv = ctx;
> +	u32 reg = *(u16 *)reg_buf;
>  	u32 *val = (u32 *)val_buf;
>  
>  	if (priv->mgmt_master &&
> -- 
> 2.41.0
> 
>