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From: Jon Hunter <jonathanh@nvidia.com>
To: Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Sameer Pujar <spujar@nvidia.com>, Vinod Koul <vkoul@kernel.org>
Cc: <dan.j.williams@intel.com>, <tiwai@suse.com>,
	<dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<sharadg@nvidia.com>, <rlokhande@nvidia.com>,
	<dramesh@nvidia.com>, <mkumard@nvidia.com>,
	linux-tegra <linux-tegra@vger.kernel.org>
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member
Date: Thu, 6 Jun 2019 11:49:16 +0100
Message-ID: <a36302fc-3173-070b-5c97-7d2c55d5e2cc@nvidia.com> (raw)
In-Reply-To: <3f836a10-eaf3-f59b-7170-6fe937cf2e43@ti.com>


On 06/06/2019 11:22, Peter Ujfalusi wrote:

...

>>>> It does sounds like that FIFO_SIZE == src/dst_maxburst in your case as
>>>> well.
>>> Not exactly equal.
>>> ADMA burst_size can range from 1(WORD) to 16(WORDS)
>>> FIFO_SIZE can be adjusted from 16(WORDS) to 1024(WORDS) [can vary in
>>> multiples of 16]
>>
>> So I think that the key thing to highlight here, is that the as Sameer
>> highlighted above for the Tegra ADMA there are two values that need to
>> be programmed; the DMA client FIFO size and the max burst size. The ADMA
>> has register fields for both of these.
> 
> How does the ADMA uses the 'client FIFO size' and 'max burst size'
> values and what is the relation of these values to the peripheral side
> (ADMAIF)?

Per Sameer's previous comment, the FIFO size is used by the ADMA to
determine how much space is available in the FIFO. I assume the burst
size just limits how much data is transferred per transaction.

>> As you can see from the above the FIFO size can be much greater than the
>> burst size and so ideally both of these values would be passed to the DMA.
>>
>> We could get by with just passing the FIFO size (as the max burst size)
>> and then have the DMA driver set the max burst size depending on this,
>> but this does feel quite correct for this DMA. Hence, ideally, we would
>> like to pass both.
>>
>> We are also open to other ideas.
> 
> I can not find public documentation (I think they are walled off by
> registration), but correct me if I'm wrong:

No unfortunately, you are not wrong here :-(

> ADMAIF - peripheral side
>  - kind of a small DMA for audio preipheral(s)?

Yes this is the interface to the APE (audio processing engine) and data
sent to the ADMAIF is then sent across a crossbar to one of many
devices/interfaces (I2S, DMIC, etc). Basically a large mux that is user
configurable depending on the use-case.

>  - Variable FIFO size

Yes.

>  - sends DMA request to ADMA per words

From Sameer's notes it says the ADMAIF send a signal to the ADMA per
word, yes.

> ADMA - system DMA
>  - receives the DMA requests from ADMAIF
>  - counts the requests
>  - based on some threshold of the counter it will send/read from ADMAIF?
>   - maxburst number of words probably?

Sounds about right to me.

> ADMA needs to know the ADMAIF's FIFO size because, it is the one who is
> managing that FIFO from the outside, making sure that it does not over
> or underrun?

Yes.

> And it is the one who sets the pace (in effect the DMA burst size - how
> many bytes the DMA jumps between refills) of refills to the ADMAIF's FIFO?

Yes.

So currently, if you look at the ADMA driver
(drivers/dma/tegra210-adma.c) you will see we use the src/dst_maxburst
for the burst, but the FIFO size is hard-coded (see the
TEGRA210_FIFO_CTRL_DEFAULT and TEGRA186_FIFO_CTRL_DEFAULT definitions).
Ideally, we should not hard-code this but pass it.

Given that there are no current users of the ADMA upstream, we could
change the usage of the src/dst_maxburst, but being able to set the FIFO
size as well would be ideal.

Cheers
Jon

-- 
nvpublic

  reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-30 11:30 Sameer Pujar
2019-04-30 11:30 ` [PATCH] " Sameer Pujar
2019-05-02  6:04 ` Vinod Koul
2019-05-02  6:04   ` [PATCH] " Vinod Koul
2019-05-02 10:53   ` Sameer Pujar
2019-05-02 12:25     ` Vinod Koul
2019-05-02 13:29       ` Sameer Pujar
2019-05-03 19:10         ` Peter Ujfalusi
2019-05-04 10:23         ` Vinod Koul
2019-05-06 13:04           ` Sameer Pujar
2019-05-06 15:50             ` Vinod Koul
2019-06-06  3:49               ` Sameer Pujar
2019-06-06  6:00                 ` Peter Ujfalusi
2019-06-06  6:41                   ` Sameer Pujar
2019-06-06  7:14                     ` Jon Hunter
2019-06-06 10:22                       ` Peter Ujfalusi
2019-06-06 10:49                         ` Jon Hunter [this message]
2019-06-06 11:54                           ` Peter Ujfalusi
2019-06-06 12:37                             ` Jon Hunter
2019-06-06 13:45                               ` Dmitry Osipenko
2019-06-06 13:55                                 ` Dmitry Osipenko
2019-06-06 14:26                                   ` Jon Hunter
2019-06-06 14:36                                     ` Jon Hunter
2019-06-06 14:36                                     ` Dmitry Osipenko
2019-06-06 14:47                                       ` Jon Hunter
2019-06-06 14:25                                 ` Jon Hunter
2019-06-06 15:18                                   ` Dmitry Osipenko
2019-06-06 16:32                                     ` Jon Hunter
2019-06-06 16:44                                       ` Dmitry Osipenko
2019-06-06 16:53                                         ` Jon Hunter
2019-06-06 17:25                                           ` Dmitry Osipenko
2019-06-06 17:56                                             ` Dmitry Osipenko
2019-06-07  9:24                                             ` Jon Hunter
2019-06-07  5:50                               ` Peter Ujfalusi
2019-06-07  9:18                                 ` Jon Hunter
2019-06-07 10:27                                   ` Jon Hunter
2019-06-07 12:17                                     ` Peter Ujfalusi
2019-06-07 12:58                                       ` Jon Hunter
2019-06-07 13:35                                         ` Peter Ujfalusi
2019-06-07 20:53                                           ` Dmitry Osipenko
2019-06-10  8:01                                             ` Jon Hunter
2019-06-10  7:59                                           ` Jon Hunter
2019-06-13  4:43                 ` Vinod Koul
2019-06-17  7:07                   ` Sameer Pujar
2019-06-18  4:33                     ` Vinod Koul
2019-06-20 10:29                       ` Sameer Pujar
2019-06-24  6:26                         ` Vinod Koul
2019-06-25  2:57                           ` Sameer Pujar
2019-07-05  6:15                             ` Sameer Pujar
2019-07-15 15:42                               ` Sameer Pujar
2019-07-19  5:04                               ` Vinod Koul
2019-07-23  5:54                                 ` Sameer Pujar
2019-07-29  6:10                                   ` Vinod Koul
2019-07-31  9:48                                     ` Jon Hunter
2019-07-31 15:16                                       ` Vinod Koul
2019-08-02  8:51                                         ` Jon Hunter
2019-08-08 12:38                                           ` Vinod Koul
2019-08-19 15:56                                             ` Jon Hunter
2019-08-20 11:05                                               ` Vinod Koul

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