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From: Vinod Koul <vkoul@kernel.org>
To: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: dan.j.williams@intel.com, dmaengine@vger.kernel.org,
	andriy.shevchenko@linux.intel.com
Subject: Re: [PATCH] dmaengine: dmatest: Add support for completion polling
Date: Tue, 4 Jun 2019 18:15:27 +0530	[thread overview]
Message-ID: <20190604124527.GG15118@vkoul-mobl> (raw)
In-Reply-To: <793f9f48-0609-4aa5-2688-bf30525e229c@ti.com>

On 03-06-19, 10:05, Peter Ujfalusi wrote:

> > I think the main question is how polling for completion should be
> > handled when client does not request for completion interrupt, thus we
> > will have no callback in the DMA driver when the transfer is completed.
> > 
> > If DMA_PREP_INTERRUPT is set for the tx_descriptor then the polling will
> > wait until the DMA driver internally receives the interrupt that the
> > transfer is done and sets the cookie to completed state.
> > 
> > However if DMA_PREP_INTERRUPT is not set, the DMA driver will not get
> > notification from the HW that is the transfer is done, the only way to
> > know is to check the tx_status and based on the residue (if it is 0 then
> > it is done) decide what to tell the client.
> > 
> > Should the client call dmaengine_terminate_* after the polling returned
> > unconditionally to free up the descriptor?
> 
> This is how omap-dma is handling the polled memcpy support.

Yes that is a good question. Even if the client does not set
DMA_PREP_INTERRUPT would there be no interrupt generated by controller
on txn completion? If not how will next txn be submitted to the
hardware.

I think we should view DMA_PREP_INTERRUPT from client pov, but
controller cannot get away with disabling interrupts IMO.

Assuming I had enough caffeine before I thought process, then client would
poll descriptor status using cookie and should free up once the cookie
is freed, makes sense?

-- 
~Vinod

  reply	other threads:[~2019-06-04 12:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29  8:37 [PATCH] dmaengine: dmatest: Add support for completion polling Peter Ujfalusi
2019-05-31  6:54 ` Peter Ujfalusi
2019-06-03  7:05   ` Peter Ujfalusi
2019-06-04 12:45     ` Vinod Koul [this message]
2019-06-04 13:35       ` Peter Ujfalusi
2019-06-10  7:04         ` Vinod Koul
2019-06-10 11:12           ` Peter Ujfalusi
2019-06-11  4:47             ` Vinod Koul
2019-06-11 13:41               ` Peter Ujfalusi

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