dmaengine Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Ujfalusi <peter.ujfalusi@ti.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Vinod Koul <vkoul@kernel.org>, <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: Fri, 24 Jan 2020 09:38:50 +0200
Message-ID: <7216460c-799f-efc7-c8be-9dd9b9829d10@ti.com> (raw)
In-Reply-To: <ded9c051-11f3-e61a-e0de-1cd54a8c85d5@ti.com>



On 24/01/2020 9.20, Peter Ujfalusi wrote:
> Hi Laurent,
> 
> On 23/01/2020 14.23, Laurent Pinchart wrote:
>>>>> 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.
> 
> You have a special hardware in hand, most DMAs can not just replace a
> cyclic transfer in-flight and it also kind of violates the DMAengine
> principles.

Is there any specific reason why you need DMAengine driver for a display
DMA? Usually the drm drivers handle their DMA internally.

> If cyclic transfer is started then it is expected to run forever until
> it is terminated. Preparing and issuing a new transfer will not get
> executed when there is already a cyclic transfer in flight as your only
> option is to terminate_all, which will kill the running cyclic _and_
> will discard the issued and pending transfers.
> 
> So the use case is page flip when you have multiple framebuffers and you
> switch them to show the updated one, right?
> 
> There are things missing in DMAengine in API level for sure to do this,
> imho.
> The issue is that cyclic transfers will never complete, they run until
> terminated, but you want to replace the currently executing one with a
> another cyclic transfer without actually terminating the other.
> 
> It is like pause the 1st cyclic and continue with the 2nd one. Then at
> some point you pause the 2nd one and restart the 1st one.
> It is also crucial that the pause /switch happens when the executing one
> finished the interleaved round and not in the middle somewhere, right?
> 
> If you:
> desc_1 = dmaengine_prep_interleaved_cyclic(chan, );
> cookie_1 = dmaengine_submit(desc_1);
> desc_2 = dmaengine_prep_interleaved_cyclic(chan, );
> cookie_2 = dmaengine_submit(desc_1);
> 
> /* cookie_1/desc_1 is started */
> dma_async_issue_pending(chan);
> 
> /* When need to switch to cookie_2 */
> dmaengine_cyclic_set_active_cookie(chan, cookie_2);
> /*
>  * cookie_1 execution is suspended after it finished the running
>  * dma_interleaved_template or buffer in normal cyclic and cookie_2
>  * is replacing it.
>  */
> 
> /* Switch back to cookie_1 */
> dmaengine_cyclic_set_active_cookie(chan, cookie_1);
> /*
>  * cookie_2 execution is suspended after it finished the running
>  * dma_interleaved_template or buffer in normal cyclic and cookie_1
>  * is replacing it.
>  */
> 
> There should be a (yet another) capabilities flag got
> cyclic_set_active_cookie and the documentation should be strict on what
> is the expected behavior.
> 
> You can kill everything with terminate_all.
> There is another thing which is missing imho from DMAengine: to
> terminate a specific cookie, not the entire channel, which might be a
> good addition as you might spawn framebuffers and then delete them and
> you might want to release the corresponding cookie/descriptor as well.

This is a bit trickier as DMAengine's cookie is s32 and internally
treated as a running number and cookie status is checked against s32
numbers with < >, I think this will not like when someone kills a cookie
in the middle.

> 
> What do you think?
> 
> - Péter
> 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
> 

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

  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
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 [this message]
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=7216460c-799f-efc7-c8be-9dd9b9829d10@ti.com \
    --to=peter.ujfalusi@ti.com \
    --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=tejasu@xilinx.com \
    --cc=vkoul@kernel.org \
    /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