Re: [PATCH v2][next] wifi: ath6kl: wmi: Avoid -Wflex-array-member-not-at-end warning

[Jeff Johnson <jeff.johnson@oss.qualcomm.com>]

On 2/18/2026 1:38 AM, Gustavo A. R. Silva wrote:
> 
>>> @@ -1652,7 +1656,7 @@ struct roam_ctrl_cmd {
>>>   	union {
>>>   		u8 bssid[ETH_ALEN]; /* WMI_FORCE_ROAM */
>>>   		u8 roam_mode; /* WMI_SET_ROAM_MODE */
>>> -		struct bss_bias_info bss; /* WMI_SET_HOST_BIAS */
>>> +		struct bss_bias_info_hdr bss; /* WMI_SET_HOST_BIAS */
>>>   		struct low_rssi_scan_params params; /* WMI_SET_LRSSI_SCAN_PARAMS
>>>   						     */
>>>   	} __packed info;
>>
>> That bss member appears to be completely unused
>> (bssid, roam_mode, and params are used)
>>
>> So IMO the better solution is to remove bss from the union.
>> And I think struct bss_bias and struct bss_bias_info can also be removed.
> 
> Even if they're not used, are you sure they aren't there simply	
> to define the memory layout of struct roam_ctrl_cmd?
> 
> As Kees commented[1], struct roam_ctrl_cmd appears to be a
> hardware interface... See below:
> 
> drivers/net/wireless/ath/ath6kl/wmi.c:
>   755 /*
>   756  * Mechanism to modify the roaming behavior in the firmware. The lower rssi
>   757  * at which the station has to roam can be passed with
>   758  * WMI_SET_LRSSI_SCAN_PARAMS. Subtract 96 from RSSI to get the signal level
>   759  * in dBm.
>   760  */
>   761 int ath6kl_wmi_set_roam_lrssi_cmd(struct wmi *wmi, u8 lrssi)
>   762 {
>   763         struct sk_buff *skb;
>   764         struct roam_ctrl_cmd *cmd;
>   765
>   766         skb = ath6kl_wmi_get_new_buf(sizeof(*cmd));
>   767         if (!skb)
>   768                 return -ENOMEM;
>   769
>   770         cmd = (struct roam_ctrl_cmd *) skb->data;
> ...
> }

yes, it defines a hardware interface. But note the 'info' is a union, and each
member of the union is there to support a specific value of roam_ctrl. And
since the WMI_SET_HOST_BIAS roam_ctrl is not used, the only important thing to
consider with your patch is that the location of the roam_ctrl field must not
change, and hence the size of union info must not change.

pahole of the original:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct bss_bias_info bss;                /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

pahole with struct bss removed:
struct roam_ctrl_cmd {
	union {
		u8                 bssid[6];             /*     0     6 */
		u8                 roam_mode;            /*     0     1 */
		struct low_rssi_scan_params params;      /*     0     8 */
	} info;                                          /*     0     8 */
	u8                         roam_ctrl;            /*     8     1 */

	/* size: 9, cachelines: 1, members: 2 */
	/* last cacheline: 9 bytes */
} __attribute__((__packed__));

So the size of the message and the location of roam_ctrl is unchanged.

/jeff