linux-kernel - RE: [PATCH 1/3] dmaengine: xilinx_dma: Check for channel idle state before submitting dma descriptor

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Date:   Mon, 19 Dec 2016 15:39:43 +0000
From:   Appana Durga Kedareswara Rao <appana.durga.rao@...inx.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vinod.koul@...el.com" <vinod.koul@...el.com>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        Soren Brinkmann <sorenb@...inx.com>,
        "moritz.fischer@...us.com" <moritz.fischer@...us.com>,
        "luis@...ethencourt.com" <luis@...ethencourt.com>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] dmaengine: xilinx_dma: Check for channel idle state
 before submitting dma descriptor

Hi Laurent Pinchart,

	Thanks for the review...

> >
> > +	if (!chan->idle)
> > +		return;
> 
> Don't you need to perform the same check for the DMA and CDMA channels ? If
> so, shouldn't this be moved to common code ?

Will fix it in v2...

> 
> There's another problem (not strictly introduced by this patch) I wanted to
> mention. The append_desc_queue() function, called from your tx_submit
> handler, appends descriptors to the pending_list. The DMA engine API states
> that a transfer submitted by tx_submit will not be executed until .issue_pending()
> is called. However, if a transfer is in progress at tx_submit time, I believe that
> the IRQ handler, at transfer completion, will start the next transfer from the
> pending_list even if .issue_pending() hasn't been called for it.
> 
> >  	if (list_empty(&chan->pending_list))
> >  		return;


If user submits more than h/w limit then that case only driver will process
The descriptors from the pending_list for other cases the pending_list will be 
Empty so driver just returns from there.

> 
> Now that you catch busy channels with a software flag, do you still need the
> xilinx_dma_is_running() and xilinx_dma_is_idle() checks ? Three different checks
> for the same or very similar conditions are confusing, if you really need them
> you should document clearly how they differ.

Will remove the xilinx_dma_is_running and xilinx_dmais_idle() checks and will use
Chan->idle check across all the IP's. Will fix it v2...

> 
> > @@ -1110,6 +1116,7 @@ static void xilinx_vdma_start_transfer(struct
> > xilinx_dma_chan *chan) vdma_desc_write(chan, XILINX_DMA_REG_VSIZE,
> > last->hw.vsize);
> >  	}
> >
> > +	chan->idle = false;
> 
> (and this too)

Will fix in v2...

Regards,
Kedar.