linux-kernel - Re: [PATCH 1/7] k3dma: Fix hisi burst clipping

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Message-ID: <20160805033610.GK9681@localhost>
Date:	Fri, 5 Aug 2016 09:06:10 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andy Green <andy.green@...aro.org>,
	Zhangfei Gao <zhangfei.gao@...aro.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Mark Brown <broonie@...nel.org>, Andy Green <andy@...mcat.com>
Subject: Re: [PATCH 1/7] k3dma: Fix hisi burst clipping

On Thu, Aug 04, 2016 at 10:36:32AM -0700, John Stultz wrote:
> On Thu, Aug 4, 2016 at 6:08 AM, Vinod Koul <vinod.koul@...el.com> wrote:
> > On Fri, Jul 29, 2016 at 03:40:46PM -0700, John Stultz wrote:
> >> On Sun, Jul 24, 2016 at 12:25 AM, Vinod Koul <vinod.koul@...el.com> wrote:
> >> > On Wed, Jul 20, 2016 at 08:53:03PM -0700, John Stultz wrote:
> >> >> From: Andy Green <andy.green@...aro.org>
> >> >>
> >> >> Max burst len is a 4-bit field, but at the moment it's clipped with
> >> >> a 5-bit constant... reduce it to that which can be expressed
> >> >
> >> > Maybe we should GENMASK() etc to avoid these errors..
> >>
> >> Not sure I follow what you're thinking here... can you clarify a bit?
> >
> > I am assuming the 4bit field was a mistake by orignal author. Using GENMASK,
> > BIT etc macro helps you to avoid those as one would look at datasheet and
> > say this is specfied as bit 5 thru 9, so let me say GENMASK(5, 0) rather
> > than a typo which missed 5th bit.
> >
> > But ofcourse if the error was due to some other reason then this one doesnt
> > help.
> 
> It was more that in taking the cfg->src/dst_maxburst value and setting
> it as a value that can be represented in 4 bits for the hardware:
>         if ((maxburst == 0) || (maxburst > 16))
>                 val = 16;
>         else
>                 val = maxburst - 1;
> 
> However, the logic error is trying to set the value to 16 if maxburst
> is larger then 16, when 16 is 5 bits, when 15 is the largest value we
> can express in 4 bits.
> 
> So I'm not sure how GENMASK() would be particularly useful (I guess
> using val = GENMASK(4,0) instead of val = 15?). But I'm not sure that
> makes the code any clearer.

Looks like this was latter case, so it doesnt seem to help here

-- 
~Vinod