linux-kernel - Re: [PATCH] regmap: flat: introduce register striding to save somememories

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Message-ID: <20151218082321.GW5727@sirena.org.uk>
Date:	Fri, 18 Dec 2015 08:23:21 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Xiubo Li <lixiubo@...s.chinamobile.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regmap: flat: introduce register striding to save
 somememories

On Tue, Dec 15, 2015 at 04:37:12PM +0800, Xiubo Li wrote:
> On 15/12/2015 01:57, Mark Brown wrote:
> >On Mon, Dec 14, 2015 at 03:14:34PM +0800, Xiubo Li wrote:

> >I'm guessing for your particular register maps the performance isn't too
> >big an issue...  do you have any numbers for how much space you're
> >saving overall?

> Not yet, but maybe in the future we could see a larger register
> striding, like 32 for MMIO using flat cache.

OK, well I'd like to se 

> >Is it worth finding a way to make this possible to
> >enable on maps that benefit?

> I'm thinking to use the bit rotation to improve the performance of
> the whole regmap.

> like:
> if(reg % reg_stride) --> if(!IS_ALIGNED(reg, reg_stride))
> ...
> index = reg / reg_stride; --> index = reg >> reg_stride_order;
> 
> And do you have any comment and suggestion for the above?

I think we'll need to continue supporting non power of two strides so
an unconditional conversion to shifts might be an issue - some weird DSP
probably does that.

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