From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>,
dmaengine@vger.kernel.org, Michal Simek <michal.simek@xilinx.com>,
Hyun Kwon <hyun.kwon@xilinx.com>,
Tejas Upadhyay <tejasu@xilinx.com>,
Satish Kumar Nagireddy <SATISHNA@xilinx.com>
Subject: Re: [PATCH v3 2/6] dmaengine: Add interleaved cyclic transaction type
Date: Mon, 10 Feb 2020 16:06:18 +0200 [thread overview]
Message-ID: <20200210140618.GA4727@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20200124085051.GA4842@pendragon.ideasonboard.com>
Hi Vinod,
On Fri, Jan 24, 2020 at 10:50:51AM +0200, Laurent Pinchart wrote:
> On Fri, Jan 24, 2020 at 11:40:47AM +0530, Vinod Koul wrote:
> > On 23-01-20, 14:23, Laurent Pinchart wrote:
> >>>>>> @@ -701,6 +702,10 @@ struct dma_filter {
> >>>>>> * The function takes a buffer of size buf_len. The callback function will
> >>>>>> * be called after period_len bytes have been transferred.
> >>>>>> * @device_prep_interleaved_dma: Transfer expression in a generic way.
> >>>>>> + * @device_prep_interleaved_cyclic: prepares an interleaved cyclic transfer.
> >>>>>> + * This is similar to @device_prep_interleaved_dma, but the transfer is
> >>>>>> + * repeated until a new transfer is issued. This transfer type is meant
> >>>>>> + * for display.
> >>>>>
> >>>>> I think capture (camera) is another potential beneficiary of this.
> >>
> >> Possibly, although in the camera case I'd rather have the hardware stop
> >> if there's no more buffer. Requiring a buffer to always be present is
> >> annoying from a userspace point of view. For display it's different, if
> >> userspace doesn't submit a new frame, the same frame should keep being
> >> displayed on the screen.
> >>
> >>>>> So you don't need to terminate the running interleaved_cyclic and start
> >>>>> a new one, but prepare and issue a new one, which would
> >>>>> terminate/replace the currently running cyclic interleaved DMA?
> >>
> >> Correct.
> >>
> >>>> Why not explicitly terminate the transfer and start when a new one is
> >>>> issued. That can be common usage for audio and display..
> >>>
> >>> Yes, this is what I'm asking. The cyclic transfer is running and in
> >>> order to start the new transfer, the previous should stop. But in cyclic
> >>> case it is not going to happen unless it is terminated.
> >>>
> >>> When one would want to have different interleaved transfer the display
> >>> (or capture )IP needs to be reconfigured as well. The the would need to
> >>> be terminated anyways to avoid interpreting data in a wrong way.
> >>
> >> The use case here is not to switch to a new configuration, but to switch
> >> to a new buffer. If the transfer had to be terminated manually first,
> >> the DMA engine would potentially miss a frame, which is not acceptable.
> >> We need an atomic way to switch to the next transfer.
> >
> > So in this case you have, let's say a cyclic descriptor with N buffers
> > and they are cyclically capturing data and providing to client/user..
>
> For the display case it's cyclic over a single buffer that is repeatedly
> displayed over and over again until a new one replaces it, when
> userspace wants to change the content on the screen. Userspace only has
> to provide a new buffer when content changes, otherwise the display has
> to keep displaying the same one.
Is the use case clear enough, or do you need more information ? Are you
fine with the API for this kind of use case ?
> For cameras I don't think cyclic makes too much sense, except when the
> DMA engine can't work in single-shot mode and always requires a buffer
> to write into. That shouldn't be the norm.
>
> > So why would you like to submit again...? Once whole capture has
> > completed you would terminate, right...
> >
> > Sorry not able to wrap my head around why new submission is required and
> > if that is the case why previous one cant be terminated :)
--
Regards,
Laurent Pinchart
next prev parent reply other threads:[~2020-02-10 14:06 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-23 2:29 [PATCH v3 0/6] dma: Add Xilinx ZynqMP DPDMA driver Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 1/6] dt: bindings: dma: xilinx: dpdma: DT bindings for Xilinx DPDMA Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 2/6] dmaengine: Add interleaved cyclic transaction type Laurent Pinchart
2020-01-23 8:03 ` Peter Ujfalusi
2020-01-23 8:43 ` Vinod Koul
2020-01-23 8:51 ` Peter Ujfalusi
2020-01-23 12:23 ` Laurent Pinchart
2020-01-24 6:10 ` Vinod Koul
2020-01-24 8:50 ` Laurent Pinchart
2020-02-10 14:06 ` Laurent Pinchart [this message]
2020-02-13 13:29 ` Vinod Koul
2020-02-13 13:48 ` Laurent Pinchart
2020-02-13 14:07 ` Vinod Koul
2020-02-13 14:15 ` Peter Ujfalusi
2020-02-13 16:52 ` Laurent Pinchart
2020-02-14 4:23 ` Vinod Koul
2020-02-14 16:22 ` Laurent Pinchart
2020-02-17 10:00 ` Peter Ujfalusi
2020-02-19 9:25 ` Vinod Koul
2020-02-26 16:30 ` Laurent Pinchart
2020-03-02 3:47 ` Vinod Koul
2020-03-02 7:37 ` Laurent Pinchart
2020-03-03 4:32 ` Vinod Koul
2020-03-03 19:22 ` Laurent Pinchart
2020-03-04 5:13 ` Vinod Koul
2020-03-04 8:01 ` Laurent Pinchart
2020-03-04 15:37 ` Vinod Koul
2020-03-04 16:00 ` Laurent Pinchart
2020-03-04 16:24 ` Vinod Koul
[not found] ` <20200311155248.GA4772@pendragon.ideasonboard.com>
2020-03-18 15:14 ` Laurent Pinchart
2020-03-25 16:00 ` Laurent Pinchart
2020-03-26 7:02 ` Vinod Koul
2020-04-08 17:00 ` Laurent Pinchart
2020-04-15 15:12 ` Laurent Pinchart
2020-03-06 14:49 ` Peter Ujfalusi
2020-03-11 23:15 ` Laurent Pinchart
2020-02-26 16:24 ` Laurent Pinchart
2020-03-02 3:42 ` Vinod Koul
2020-01-24 7:20 ` Peter Ujfalusi
2020-01-24 7:38 ` Peter Ujfalusi
2020-01-24 8:58 ` Laurent Pinchart
2020-01-24 8:56 ` Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 3/6] dmaengine: virt-dma: Use lockdep to check locking requirements Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 4/6] dmaengine: xilinx: dpdma: Add the Xilinx DisplayPort DMA engine driver Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 5/6] dmaengine: xilinx: dpdma: Add debugfs support Laurent Pinchart
2020-01-23 2:29 ` [PATCH v3 6/6] arm64: dts: zynqmp: Add DPDMA node Laurent Pinchart
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