linux-kernel - Re: [alsa-devel] [PATCH v5 06/10] dmaengine: add API for getting dma controller's quirk

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Date:	Wed, 14 Oct 2015 16:23:10 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Shawn Lin <shawn.lin@...k-chips.com>,
	Addy Ke <addy.ke@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>, alsa-devel@...a-project.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-spi@...r.kernel.org, Doug Anderson <dianders@...omium.org>,
	Takashi Iwai <tiwai@...e.com>, dmaengine@...r.kernel.org,
	Mark Brown <broonie@...nel.org>,
	Olof Johansson <olof@...om.net>,
	Sonny Rao <sonnyrao@...omium.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [alsa-devel] [PATCH v5 06/10] dmaengine: add API for getting dma
 controller's quirk

On Thu, Oct 08, 2015 at 10:31:18AM +0200, Lars-Peter Clausen wrote:
> > Basically I agree not to expose dma's quirk to slave controllers...But, the
> > fact I mentioned on cover letter explain the reasons why I have to let slave
> > controllers know that they are working with a broken dma. It's a dilemma
> > that if we don't want that to be exposed(let slave controllers' driver get
> > the info via a API), we have t add broken quirk for all of them ,here and
> > there, which seems to be a disaster:(
> 
> The problem with this API is that it transports values with device specific
> meanings over a generic API. Which is generally speaking not a good idea
> because the consumer witch is supposed to be generic suddenly needs to know
> which provider it is talking to.
> 
> A better solution in this case typically is either introduce a generic API
> with generic values or a custom API with custom values, but don't mix the two.
> 
> > 
> > I would appreciate it if you could give me some suggestions at your earliest
> > convenience. :)
> 
> In this case I think the best way to handle this is not quirks, but rather
> expose the actual maximum burst size using the DMA capabilities API. Since
> supporting only a certain burst depth is not really a quirk. All hardware
> has a limit for this and for some it might be larger or smaller than for
> others and it might be the same IP core but the maximum size depends on some
> IP core parameters. So this should be discoverable.

yes that makes more sense than adding quirks, exposing the right values
which should be a readable property for driver will ensure it works on
system with/without quirks

-- 
~Vinod
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