netdev - Re: [PATCH net v2 1/2] net: dsa: qca8k: fix regmap bulk read/write methods on big endian systems

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Message-ID: <651e948f.1c0a0220.e602c.04aa@mx.google.com>
Date: Thu, 5 Oct 2023 12:48:45 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Marek Behún <kabel@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 1/2] net: dsa: qca8k: fix regmap bulk read/write
 methods on big endian systems

On Wed, Oct 04, 2023 at 11:19:03AM +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 correspond to the low 16-bits, but it
> 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>

Just find time to test this on a friend's big-endian device and can confirm
this fix the problem. Thanks!

Tested-by: Christian Marangi <ansuelsmth@...il.com>
Reviewed-by: Christian Marangi <ansuelsmth@...il.com>

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