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From: Vinod Koul <vkoul@kernel.org>
To: Jon Hunter <jonathanh@nvidia.com>
Cc: Sameer Pujar <spujar@nvidia.com>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>,
	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
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member
Date: Tue, 20 Aug 2019 16:35:10 +0530
Message-ID: <20190820110510.GQ12733@vkoul-mobl.Dlink> (raw)
In-Reply-To: <a93a472d-b8f7-973f-6068-607492421472@nvidia.com>

On 19-08-19, 16:56, Jon Hunter wrote:
> >>>>>>> On this, I am inclined to think that dma driver should not be involved.
> >>>>>>> The ADMAIF needs this configuration and we should take the path of
> >>>>>>> dma_router for this piece and add features like this to it
> >>>>>>
> >>>>>> Hi Vinod,
> >>>>>>
> >>>>>> The configuration is needed by both ADMA and ADMAIF. The size is
> >>>>>> configurable
> >>>>>> on ADMAIF side. ADMA needs to know this info and program accordingly.
> >>>>>
> >>>>> Well I would say client decides the settings for both DMA, DMAIF and
> >>>>> sets the peripheral accordingly as well, so client communicates the two
> >>>>> sets of info to two set of drivers
> >>>>
> >>>> That maybe, but I still don't see how the information is passed from the
> >>>> client in the first place. The current problem is that there is no means
> >>>> to pass both a max-burst size and fifo-size to the DMA driver from the
> >>>> client.
> >>>
> >>> So one thing not clear to me is why ADMA needs fifo-size, I thought it
> >>> was to program ADMAIF and if we have client programme the max-burst
> >>> size to ADMA and fifo-size to ADMAIF we wont need that. Can you please
> >>> confirm if my assumption is valid?
> >>
> >> Let me see if I can clarify ...
> >>
> >> 1. The FIFO we are discussing here resides in the ADMAIF module which is
> >>    a separate hardware block the ADMA (although the naming make this
> >>    unclear).
> >>
> >> 2. The size of FIFO in the ADMAIF is configurable and it this is
> >>    configured via the ADMAIF registers. This allows different channels
> >>    to use different FIFO sizes. Think of this as a shared memory that is
> >>    divided into n FIFOs shared between all channels.
> >>
> >> 3. The ADMA, not the ADMAIF, manages the flow to the FIFO and this is
> >>    because the ADMAIF only tells the ADMA when a word has been
> >>    read/written (depending on direction), the ADMAIF does not indicate
> >>    if the FIFO is full, empty, etc. Hence, the ADMA needs to know the
> >>    total FIFO size.
> >>
> >> So the ADMA needs to know the FIFO size so that it does not overrun the
> >> FIFO and we can also set a burst size (less than the total FIFO size)
> >> indicating how many words to transfer at a time. Hence, the two parameters.
> > 
> > Thanks, I confirm this is my understanding as well.
> > 
> > To compare to regular case for example SPI on DMA, SPI driver will
> > calculate fifo size & burst to be used and program dma (burst size) and
> > its own fifos accordingly
> > 
> > So, in your case why should the peripheral driver not calculate the fifo
> > size for both ADMA and ADMAIF and (if required it's own FIFO) and
> > program the two (ADMA and ADMAIF).
> > 
> > What is the limiting factor in this flow is not clear to me.
> 
> The FIFO size that is configured by the ADMAIF driver needs to be given
> to the ADMA driver so that it can program its registers accordingly. The
> difference here is that both the ADMA and ADMAIF need the FIFO size.

Can you please help describing what it is programming using the FIFO
size of ADMAIF?

Thanks
-- 
~Vinod

  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
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 [this message]
2019-09-16  9:02                                                 ` Sameer Pujar

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