RE: [PATCH rtw-next] wifi: rtl8xxxu: isolate the USB register buffer from CPU state

[Ping-Ke Shih]

‍김우석[학생](전자정보대학 전자공학과) <5mghybrid@xxxxxxxxx> wrote:
> Hi Ping-Ke,
> 
> > Cool. How did you dig that?
> 
> I was repeatedly power-cycling the AP to test recovery of a persistent
> queue in my project. After fixing a separate NetworkManager issue,
> some reconnect failures remained, so I started looking at the driver.
> 
> I was testing with four Raspberry Pis, and different units would hit
> the same failure across runs. On a failing unit, RF_MODE was corrupted,
> and restoring its initialized value brought reception back.
> 
> I narrowed it down to register corruption during scanning, then traced
> the register access path. That led me to usb_buf sharing a cache line
> with the mutex's waiter state, which can change while a USB transfer
> is in progress.

Does it mean that data in a cache line can't be modified while a USB
transfer? Even the data isn't a part of transferring data.
How can it affect the transfer? 

(I'm not a cache-line expert. Just try to understand the cause).

Ping-Ke