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

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

On 16/10/2026 21:05, Kim Wooseok wrote:
> Hi Bitterblue,
> 
>> Perhaps it's a silly question, but doesn't this just move the problem
>> elsewhere? Or does kmalloc_obj() guarantee that nothing else will access
>> the memory near usb_buf?
> 
> With a separately allocated kmalloc buffer, the kernel ensures that
> CPU accesses to other objects do not corrupt the DMA data through
> cache-line sharing. It provides the required alignment or bounce
> buffering, and usb_control_msg() uses this DMA mapping path.
> 
> The patch turns usb_buf from an embedded member into a standalone
> kmalloc buffer so that this guarantee applies to the buffer itself.
> 

Okay, that's good then.

>> An allocation for every register access was not happening even before
>> this patch. I guess your LLM wrote this...
> 
> I did not state that the previous code allocated a buffer on every
> register access. That sentence describes the allocation strategy for
> the newly separate buffer: allocate it once in probe and reuse it.
> 
> If any part of the explanation is unclear, please point it out and I
> will clarify it. I don't think speculation about how the text was
> written is necessary.
> 
> Wooseok