linux-kernel - Re: [PATCH] dmaengine: pxa_dma: fix the maximum requestor line

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Date:	Tue, 9 Feb 2016 20:50:07 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Daniel Mack <daniel@...que.org>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: pxa_dma: fix the maximum requestor line

On Tue, Feb 09, 2016 at 08:20:05AM +0100, Robert Jarzmik wrote:
> Vinod Koul <vinod.koul@...el.com> writes:
> 
> > On Mon, Feb 08, 2016 at 03:18:51PM +0100, Robert Jarzmik wrote:
> >> The current number of requestor lines is limited to 31. This was an
> >> error of a previous commit, as this number is platform dependent, and is
> >> actually :
> >>  - for pxa25x: 40 requestor lines
> >>  - for pxa27x: 74 requestor lines
> >>  - for pxa3xx: 100 requestor lines
> >> 
> >> As the driver doesn't need to know the exact number, but only an
> >
> > and why would that be a good assumption?
> Well, the driver doesn't use the exact value. Would that be 128, 1000 or 10000,
> it wouldn't change its behavior. The clients either pass -1UL (ie. no flow
> control) or a requestor line number.

Somehow that does not sound right to me. You seem to have no way of knowing
what is the actual max request line for a platforms. What if on pxa25x user
requests more than 40 lines?

> > Btw shouldn't this data come from DT?
> It can if you wish, but in this case I must amend the platform data case too, ie
> mmp_dma_platdata. And this has an impact on MMP architecture. I'd rather have
> the simpler approach unless you really want the exact number of requestor lines
> to be passed in platform_data+DT.

The information that you have X lines on a platform needs to be described
and queried. I see current approach error prone

-- 
~Vinod