linux-kernel - Re: [PATCH 8/8] dmaengine/dw_dmac: Add support for DMA_SLAVE

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Message-ID: <CACRpkdbY7ZOwY6GR4t+GODYL4yAdH-PXExmwp84R+Gz2W19X7w@mail.gmail.com>
Date:	Tue, 17 Jan 2012 09:49:18 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Viresh Kumar <viresh.kumar@...com>
Cc:	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Armando VISCONTI <armando.visconti@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	Vipin KUMAR <vipin.kumar@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	Deepak SIKRI <deepak.sikri@...com>,
	Vipul Kumar SAMAR <vipulkumar.samar@...com>,
	Amit VIRDI <Amit.VIRDI@...com>,
	Pratyush ANAND <pratyush.anand@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	Bhavna YADAV <bhavna.yadav@...com>,
	Vincenzo FRASCINO <Vincenzo.FRASCINO@...com>,
	Mirko GARDI <mirko.gardi@...com>
Subject: Re: [PATCH 8/8] dmaengine/dw_dmac: Add support for DMA_SLAVE_CONFIG

On Mon, Jan 16, 2012 at 12:42 PM, Viresh Kumar <viresh.kumar@...com> wrote:
> On 1/16/2012 3:20 PM, Viresh KUMAR wrote:
>> +     /*
>> +      * Fix sconfig's burst size according to dw_dmac. We need to convert
>> +      * them as: 1 -> 0, 2 -> 1, 4 -> 2, 8 -> 3, 16 -> 4.
>> +      *
>> +      * This can be done by findiding least significant bit set: n & (n - 1)
>> +      */
>> +     sconfig->src_maxburst &= sconfig->src_maxburst - 1;
>> +     sconfig->dst_maxburst &= sconfig->dst_maxburst - 1;
>
> Perhaps, this looks incorrect. It will always return 0. :(
> Can somebody suggest any inbuild function to do this, i think
>
> find_next_bit(sconfig->src_maxburst, sizeof(sconfig->src_maxburst), 0)
>
> will do it.

Are you looking for ffs() from <linus/bitops.h>?

find-first-set (the include boils down to include/asm-generic/bitops/ffs.h
if you want to check the implementation).

Linus Walleij
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