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

From: Jakub Kicinski <[email-masked]>
Date: Tue, 21 Nov 2023 15:08:59 -0800

On Mon, 20 Nov 2023 20:35:04 +0100 Christian Marangi wrote:
> It seems some arch (s390) require a more specific mask for FIELD_PREP
> and doesn't like using GENMASK(15, 2) for u16 values.
> 
> Fix the compilation error by adding the additional mask for the BITS
> that the PHY ignore and AND the passed addr with the real mask that the
> PHY will parse for the mailbox interface 4 addr to make sure extra
> values are correctly removed.

Ah. Um. Pff. Erm. I'm not sure.

Endianness is not my strong suit but this code:

	/* PHY expect addr in LE */
	addr = (__force u32)cpu_to_le32(addr); 

	/* ... use (u16)(addr)       */
	/* ... use (u16)(addr >> 16) */

does not make sense to me.

You're operating on register values here, there is no endian.
Endian only exists when you store or load from memory. IOW, this:

	addr = 0x12345678;
	print((u16)addr);
	print(addr >> 16);

will print the same exact thing regardless of the CPU endian.

Why did you put the byte swap in there?
-- 
pw-bot: cr