linux-kernel - Re: [PATCH] [RFC] dmaengine: add fifo

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Date:   Wed, 31 Jul 2019 20:46:10 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Sameer Pujar <spujar@...dia.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        dan.j.williams@...el.com, tiwai@...e.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        sharadg@...dia.com, rlokhande@...dia.com, dramesh@...dia.com,
        mkumard@...dia.com
Subject: Re: [PATCH] [RFC] dmaengine: add fifo_size member

On 31-07-19, 10:48, Jon Hunter wrote:
> 
> On 29/07/2019 07:10, Vinod Koul wrote:
> > On 23-07-19, 11:24, Sameer Pujar wrote:
> >>
> >> On 7/19/2019 10:34 AM, Vinod Koul wrote:
> >>> On 05-07-19, 11:45, Sameer Pujar wrote:
> >>>> Hi Vinod,
> >>>>
> >>>> What are your final thoughts regarding this?
> >>> Hi sameer,
> >>>
> >>> Sorry for the delay in replying
> >>>
> >>> 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?

> IMO there needs to be a way to pass vendor specific DMA configuration
> (if this information is not common) otherwise we just end up in a
> scenario like there is for the xilinx DMA driver
> (include/linux/dma/xilinx_dma.h) that has a custom API for passing this
> information.
> 
> Cheers
> Jon
> 
> -- 
> nvpublic

-- 
~Vinod