netdev - Re: [net-next PATCH] net: phy: aquantia: make mailbox interface4 lsw addr mask more specific

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Message-ID: <20231121155812.03113405@kernel.org>
Date: Tue, 21 Nov 2023 15:58:12 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Robert Marko <robimarko@...il.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kernel test robot
 <lkp@...el.com>
Subject: Re: [net-next PATCH] net: phy: aquantia: make mailbox interface4
 lsw addr mask more specific

On Wed, 22 Nov 2023 00:48:01 +0100 Christian Marangi wrote:
> > Not so sure about this one, it puts the u32 on the stack, and takes 
> > the address of it:
> > 
> > 	u32 word;
> > 
> > 	word = (__force u32)cpu_to_be32(word);
> > 	crc = crc_ccitt_false(crc, (u8 *)&word, sizeof(word));
> > 
> > so the endian will matter here. My guess is that this part is correct.  

Actually I'm wrong about this, you're reading and writing the data,
so endian conversion happens twice. Canceling itself out.

> Ehhh this is problematic. Data comes from nvmem or filesystem, in theory
> they should not be touched/converted.
> 
> nvmem_cell_read or request_firmware return pointer to u8 and it's the
> firmware (that is always in LE)
> 
> If data is not converted and passed AS IS from what is read to the
> allocated data, then data should be always swapped.
> (this PHY is fun... it's probably BE internally but expect LE stuff in
> the mailbox, as it does emit BE CRC.)
> 
> Any idea where I can verify if nvmem_cell_read or request_firmware makes
> any kind of endianess conversion on the data it does read?

The underlying storage should be byte-accessible, so neither interface
should change anything about the endian.

You should probably switch get_unaligned_le32() for reading it into 
the word variable, tho.