dmaengine Archive on lore.kernel.org
 help / color / Atom feed
From: Vinod Koul <vkoul@kernel.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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: Thu, 13 Feb 2020 19:37:09 +0530
Message-ID: <20200213140709.GH2618@vkoul-mobl> (raw)
In-Reply-To: <20200213134843.GG4833@pendragon.ideasonboard.com>

On 13-02-20, 15:48, Laurent Pinchart wrote:
> Hi Vinod,
> 
> On Thu, Feb 13, 2020 at 06:59:38PM +0530, Vinod Koul wrote:
> > On 10-02-20, 16:06, Laurent Pinchart wrote:
> > 
> > > > >> 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 ?
> > 
> > So we *know* when a new buffer is being used?
> 
> The user of the DMA engine (the DRM DPSUB driver in this case) knows
> when a new buffer needs to be used, as it receives it from userspace. In
> response, it prepares a new interleaved cyclic transaction and queues
> it. At the next IRQ, the DMA engine driver switches to the new
> transaction (the implementation is slightly more complex to handle race
> conditions, but that's the idea).
> 
> > IOW would it be possible for display (rather a dmaengine facing
> > display wrapper) to detect that we are reusing an old buffer and keep
> > the cyclic and once detected prepare a new descriptor, submit a new
> > one and then terminate old one which should trigger next transaction
> > to be submitted
> 
> I'm not sure to follow you. Do you mean that the display driver should
> submit a non-cyclic transaction for every frame, reusing the same buffer
> for every transaction, until a new buffer is available ? The issue with
> this is that if the CPU load gets high, we may miss a frame, and the
> display will break. The DPDMA hardware implements cyclic support for
> this reason, and we want to use that feature to comply with the real
> time requirements.

Sorry to cause confusion :) I mean cyclic

So, DRM DPSUB get first buffer
A.1 Prepare cyclic interleave txn
A.2 Submit the txn (it doesn't start here)
A.3 Invoke issue_pending (that starts the txn)

DRM DPSUB gets next buffer:
B.1 Prepare cyclic interleave txn
B.2 Submit the txn
B.3 Call terminate for current cyclic txn (we need an updated terminate
which terminates the current txn, right now we have terminate_all which
is a sledge hammer approach)
B.4 Next txn would start once current one is started

Does this help and make sense in your case

Thanks
-- 
~Vinod

  reply index

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
2020-02-13 13:29                 ` Vinod Koul
2020-02-13 13:48                   ` Laurent Pinchart
2020-02-13 14:07                     ` Vinod Koul [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200213140709.GH2618@vkoul-mobl \
    --to=vkoul@kernel.org \
    --cc=SATISHNA@xilinx.com \
    --cc=dmaengine@vger.kernel.org \
    --cc=hyun.kwon@xilinx.com \
    --cc=laurent.pinchart@ideasonboard.com \
    --cc=michal.simek@xilinx.com \
    --cc=peter.ujfalusi@ti.com \
    --cc=tejasu@xilinx.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

dmaengine Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/dmaengine/0 dmaengine/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dmaengine dmaengine/ https://lore.kernel.org/dmaengine \
		dmaengine@vger.kernel.org
	public-inbox-index dmaengine

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.dmaengine


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git