linux-kernel - Re: [RFC PATCH v1 1/2] rpmb: move rpmb_frame struct and constants to common header

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Message-ID: <eef5d4c5-c2b4-47e4-bd29-3cd6faa39dc9@acm.org>
Date: Mon, 15 Sep 2025 14:54:21 -0700
From: Bart Van Assche <bvanassche@....org>
To: Bean Huo <beanhuo@...pp.de>, avri.altman@....com,
 alim.akhtar@...sung.com, jejb@...ux.ibm.com, martin.petersen@...cle.com,
 can.guo@....qualcomm.com, ulf.hansson@...aro.org, jens.wiklander@...aro.org
Cc: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
 mikebi@...ron.com, lporzio@...ron.com, Bean Huo <beanhuo@...ron.com>
Subject: Re: [RFC PATCH v1 1/2] rpmb: move rpmb_frame struct and constants to
 common header

On 9/15/25 2:46 PM, Bean Huo wrote:
> + * @stuff        : stuff bytes

The above sounds vague to me ...

> +struct rpmb_frame {
> +	u8     stuff[196];
> +	u8     key_mac[32];
> +	u8     data[256];
> +	u8     nonce[16];
> +	__be32 write_counter;
> +	__be16 addr;
> +	__be16 block_count;
> +	__be16 result;
> +	__be16 req_resp;
> +} __packed;

Applying __packed to a data structure in its entirety is a bad practice
because it prevents the compiler from generating optimal code for
accessing multi-byte members on architectures that do not support
unaligned accesses. Please only apply __packed to the members that need
it and consider checking the size of the data structure with
static_assert().

Thanks,

Bart.