Re: [PATCH v3 1/3] wifi: rtw88: Move register access from rtw_bf_assoc() outside the RCU

[Martin Blumenstingl]

Hi Sascha,

On Fri, Mar 31, 2023 at 2:59 PM Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
>
> On Sun, Jan 08, 2023 at 10:13:22PM +0100, Martin Blumenstingl wrote:
> > USB and (upcoming) SDIO support may sleep in the read/write handlers.
> > Shrink the RCU critical section so it only cover the call to
> > ieee80211_find_sta() and finding the ic_vht_cap/vht_cap based on the
> > found station. This moves the chip's BFEE configuration outside the
> > rcu_read_lock section and thus prevent "scheduling while atomic" or
> > "Voluntary context switch within RCU read-side critical section!"
> > warnings when accessing the registers using an SDIO card (which is
> > where this issue has been spotted in the real world - but it also
> > affects USB cards).
>
> Unfortunately this introduces a regression on my RTW8821CU chip. With
> this it constantly looses connection to the AP and reconnects shortly
> after:
Sorry to hear this! This is odd and unfortunately I don't understand
the reason for this.
rtw_bf_assoc() is only called from
drivers/net/wireless/realtek/rtw88/mac80211.c with rtwdev->mutex held.
So I don't think that it's a race condition.

There's a module parameter which lets you enable/disable BF support:
$ git grep rtw_bf_support drivers/net/wireless/realtek/rtw88/ | grep param
drivers/net/wireless/realtek/rtw88/main.c:module_param_named(support_bf,
rtw_bf_support, bool, 0644);

Have you tried disabling BF support?
Also +Cc Jernej in case he has an idea.


Best regards,
Martin