Re: [PATCH v3 2/3] mailbox: mediatek: add support for adsp mailbox controller

[allen-kh.cheng <allen-kh.cheng@mediatek.com>]

On Thu, 2021-11-25 at 14:23 +0800, Tzung-Bi Shih wrote:
> > On Thu, Nov 25, 2021 at 09:51:27AM +0800, allen-kh.cheng wrote:
> > > > On Wed, 2021-11-24 at 18:25 +0800, Tzung-Bi Shih wrote:
> > > > > > > > On Wed, Nov 24, 2021 at 04:45:13PM +0800, allen-
> > > > kh.cheng wrote:
> > > > > > > > > > > > +static int mtk_adsp_mbox_send_data(struct
> > > > > > mbox_chan *chan,
> > > > 
> > > > > > > >
> > > > > > > > void
> > > > > > > > > > > > *data)
> > > > > > > > > > > > +{
> > > > > > > > > > > > +  struct adsp_mbox_ch_info *ch_info = chan-
> > > > > > >con_priv;
> > > > > > > > > > > > +  void __iomem *reg = ch_info->va_reg;
> > > > > > > > > > > > +
> > > > > > > > > > > > +  spin_lock(&ch_info->lock);
> > > > > > > > > > > > +  writel(ch_info->ipc_op_val, reg +
> > > > > > MTK_ADSP_MBOX_IN_CMD);
> > > > > > > > > > > > +  spin_unlock(&ch_info->lock);
> > > > 
> > > > > > > >
> > > > > > > > Why does it need the lock?
> > > > > > > >
> > > > > > > > Is the write to MTK_ADSP_MBOX_IN_CMD a synchronous
> > > > operation?
> > > > > > > > - If yes, I failed to understand why does it need the
> > > > > > > > lock.  Every
> > > > > > > > calls to mtk_adsp_mbox_send_data() should wait for the
> > > > data
> > > 
> > > > > >
> > > > > > transfer
> > > > > > > > completion.
> > > > > > > > - If no, I also failed to understand
> > > 
> > > > > >
> > > > > > why.  mtk_adsp_mbox_send_data()
> > > > > > > > has no way to be aware of the transfer
> > > > completion.  Would
> > > > > > > > expect a
> > > > > > > > loop for checking the completion for the case.
> > > > > > > >
> > > 
> > > > > >
> > > > > >  
> > 
> > > >
> > > > In ADSP MBOX IPC flow,
> > > >  
> > > > Host would call mbox send data when the shared data transfer
> > > > completed.
> > > >  
> > > > (mtk_adsp_mbox_send_data will notice client using
> > > > MTK_ADSP_MBOX_IN_CMD)
> > > >  
> > > > It’s more like a signal.
> > > >  
> > > > In general case,
> > > >  
> > > > There may be some hosts use the same mbox channel.
> > > >  
> > > > I think it’s better using lock to protect access to
> > > > MTK_ADSP_MBOX_IN_CMD registers
> 
> >
> > I still failed to understand.  What if 2 hosts notify the same
> client
> > by writing MTK_ADSP_MBOX_IN_CMD at the same time?

 
Hi Tzung-Bi,
 
After I think carefully. There is no need to add lock in
mtk_adsp_mbox_send_data.
 
In our dsp ipc design, we only have one host(ap) and one client(dsp).
 
If sof ip message transfer is complete, host will use mbox notice dsp
message arrived.
 
(MTK_ADSP_MBOX_IN_CMD is signal to trigger mbox irq)
 
I will remove this in next version.