linux-kernel - Re: [PATCH net-next v4] net: marvell: prestera: add firmware v4.0 support

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Date:   Thu, 4 Nov 2021 19:59:20 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Volodymyr Mytnyk <volodymyr.mytnyk@...ision.eu>
Cc:     kuba@...nel.org, andrew@...n.ch, mickeyr@...vell.com,
        serhiy.pshyk@...ision.eu, taras.chornyi@...ision.eu,
        Volodymyr Mytnyk <vmytnyk@...vell.com>,
        Vadym Kochan <vkochan@...vell.com>,
        Yevhen Orlov <yevhen.orlov@...ision.eu>,
        Taras Chornyi <tchornyi@...vell.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4] net: marvell: prestera: add firmware v4.0
 support

On Fri, Oct 29, 2021 at 08:38:07AM +0300, Volodymyr Mytnyk wrote:
> From: Volodymyr Mytnyk <vmytnyk@...vell.com>
> 
> Add firmware (FW) version 4.0 support for Marvell Prestera
> driver.
> 
> Major changes have been made to new v4.0 FW ABI to add support
> of new features, introduce the stability of the FW ABI and ensure
> better forward compatibility for the future driver vesrions.
> 
> Current v4.0 FW feature set support does not expect any changes
> to ABI, as it was defined and tested through long period of time.
> The ABI may be extended in case of new features, but it will not
> break the backward compatibility.
> 
> ABI major changes done in v4.0:
> - L1 ABI, where MAC and PHY API configuration are split.
> - ACL has been split to low-level TCAM and Counters ABI
>   to provide more HW ACL capabilities for future driver
>   versions.
> 
> To support backward support, the addition compatibility layer is
> required in the driver which will have two different codebase under
> "if FW-VER elif FW-VER else" conditions that will be removed
> in the future anyway, So, the idea was to break backward support
> and focus on more stable FW instead of supporting old version
> with very minimal and limited set of features/capabilities.
> 
> Improve FW msg validation:
>  * Use __le64, __le32, __le16 types in msg to/from FW to
>    catch endian mismatch by sparse.
>  * Use BUILD_BUG_ON for structures sent/recv to/from FW.
> 
> Co-developed-by: Vadym Kochan <vkochan@...vell.com>
> Signed-off-by: Vadym Kochan <vkochan@...vell.com>
> Signed-off-by: Yevhen Orlov <yevhen.orlov@...ision.eu>
> Signed-off-by: Taras Chornyi <tchornyi@...vell.com>
> Signed-off-by: Volodymyr Mytnyk <vmytnyk@...vell.com>

Compiling this file on m68k results in:

In file included from <command-line>:
In function 'prestera_hw_build_tests',
    inlined from 'prestera_hw_switch_init' at drivers/net/ethernet/marvell/prestera/prestera_hw.c:788:2:
include/linux/compiler_types.h:317:45: error: call to '__compiletime_assert_351' declared with attribute error: BUILD_BUG_ON failed: sizeof(struct prestera_msg_switch_attr_req) != 16

The size of struct prestera_msg_switch_attr_req is not well defined.

struct prestera_msg_switch_attr_req {
        struct prestera_msg_cmd cmd;			// 4 bytes
        __le32 attr;					// 4 bytes
        union prestera_msg_switch_param param;		// 6 bytes
};

The compiler may well decide, in this situation, to generate a structure of
size 14, not 16. The error is therefore not surprising.

Guenter