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From: Sameer Pujar <spujar@nvidia.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: <dan.j.williams@intel.com>, <tiwai@suse.com>,
	<jonathanh@nvidia.com>, <dmaengine@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member
Date: Thu, 2 May 2019 18:59:09 +0530
Message-ID: <3368d1e1-0d7f-f602-5b96-a978fcf4d91b@nvidia.com> (raw)
In-Reply-To: <20190502122506.GP3845@vkoul-mobl.Dlink>


On 5/2/2019 5:55 PM, Vinod Koul wrote:
> On 02-05-19, 16:23, Sameer Pujar wrote:
>> On 5/2/2019 11:34 AM, Vinod Koul wrote:
>>> On 30-04-19, 17:00, Sameer Pujar wrote:
>>>> During the DMA transfers from memory to I/O, it was observed that transfers
>>>> were inconsistent and resulted in glitches for audio playback. It happened
>>>> because fifo size on DMA did not match with slave channel configuration.
>>>>
>>>> currently 'dma_slave_config' structure does not have a field for fifo size.
>>>> Hence the platform pcm driver cannot pass the fifo size as a slave_config.
>>>> Note that 'snd_dmaengine_dai_dma_data' structure has fifo_size field which
>>>> cannot be used to pass the size info. This patch introduces fifo_size field
>>>> and the same can be populated on slave side. Users can set required size
>>>> for slave peripheral (multiple channels can be independently running with
>>>> different fifo sizes) and the corresponding sizes are programmed through
>>>> dma_slave_config on DMA side.
>>> FIFO size is a hardware property not sure why you would want an
>>> interface to program that?
>>>
>>> On mismatch, I guess you need to take care of src/dst_maxburst..
>> Yes, FIFO size is a HW property. But it is SW configurable(atleast in my
>> case) on
>> slave side and can be set to different sizes. The src/dst_maxburst is
> Are you sure, have you talked to HW folks on that? IIUC you are
> programming the data to be used in FIFO not the FIFO length!
Yes, I mentioned about FIFO length.

1. MAX FIFO size is fixed in HW. But there is a way to limit the usage 
per channel
    in multiples of 64 bytes.
2. Having a separate member would give independent control over MAX 
BURST SIZE and
    FIFO SIZE.
>
>> programmed
>> for specific values, I think this depends on few factors related to
>> bandwidth
>> needs of client, DMA needs of the system etc.,
> Precisely
>
>> In such cases how does DMA know the actual FIFO depth of slave peripheral?
> Why should DMA know? Its job is to push/pull data as configured by
> peripheral driver. The peripheral driver knows and configures DMA
> accordingly.
I am not sure if there is any HW logic that mandates DMA to know the size
of configured FIFO depth on slave side. I will speak to HW folks and
would update here.
>   
>>>> Request for feedback/suggestions.
>>>>
>>>> Signed-off-by: Sameer Pujar <spujar@nvidia.com>
>>>> ---
>>>>    include/linux/dmaengine.h | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>>>> index d49ec5c..9ec198b 100644
>>>> --- a/include/linux/dmaengine.h
>>>> +++ b/include/linux/dmaengine.h
>>>> @@ -351,6 +351,8 @@ enum dma_slave_buswidth {
>>>>     * @slave_id: Slave requester id. Only valid for slave channels. The dma
>>>>     * slave peripheral will have unique id as dma requester which need to be
>>>>     * pass as slave config.
>>>> + * @fifo_size: Fifo size value. The dma slave peripheral can configure required
>>>> + * fifo size and the same needs to be passed as slave config.
>>>>     *
>>>>     * This struct is passed in as configuration data to a DMA engine
>>>>     * in order to set up a certain channel for DMA transport at runtime.
>>>> @@ -376,6 +378,7 @@ struct dma_slave_config {
>>>>    	u32 dst_port_window_size;
>>>>    	bool device_fc;
>>>>    	unsigned int slave_id;
>>>> +	u32 fifo_size;
>>>>    };
>>>>    /**
>>>> -- 
>>>> 2.7.4

  reply index

Thread overview: 60+ 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 [this message]
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
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
2019-09-16  9:02                                                 ` Sameer Pujar

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