On June 17, 2024 3:19:56 PM Kalle Valo <kvalo@xxxxxxxxxx> wrote:
Kurt Van Dijck <dev.kurt@xxxxxxxxxxxxxxxxxxxxxx> writes:/* context */We (Yamabiko) have an application where we migrated to a bcm4339 sdio wifi chip.We use it in AP+STA mode: when the chip is detected (wlan+ add uevent), we call 'run iw dev wlan0 interface add wap0 type __ap' and start wpa_supplicant on wlan0 and hostapd on wap0. The STA is more important than the AP. We have 'roamoff' parameter set. We observed problems with the firmware roaming before and switched to wpa_supplicant roaming. We run a linux v5.4.24 derivative. /* problem */ We observed that the chip is able to switch channel for wpa_supplicant to connect to a different channel, but it soon looses connection because hostapd does not change channel too.This did work with our previous wifi chip (realtek 88x2 something), which notifieshostapd that it switched. /* patch description */ I went down and ended up modifying the brcmfmac driver, patch appended below. For contributing on these mailing lists, I ported it to yesterday's master. The idea is that whenever a STA issues a connect with channel info, the AP'swill switch to it too. This implies a small glitch in the AP radio, which already occurred before my patch. it seems that the wifi chip cannot modify radio settings per virtual interface, although the API to the wifi chip suggests it can (that is most probable a more generic communication used for other chips that can do this).The channel switch is also reported to userspace. To be less invasive, this new behaviour is put behind a module parameter 'ap_follow_sta'.FWIW module parameters should be avoided, especially for 802.11 protocol level functionality.
Right. Only had taken a quick glance and noticed this. The 802.11 spec does not really cover the concept of virtual interfaces, but still having this solved through a module parameter for a specific driver is definitely not a first choice.
Anyway, I do have some thoughts about this patch. Hopefully I can dive into this in coming days.
Regards, Arend
-- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
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