linux-kernel - Re: [PATCH 2/2] dw_dmac: return proper residue value

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Date:	Wed, 23 Jan 2013 12:20:52 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCH 2/2] dw_dmac: return proper residue value

On Wed, Jan 23, 2013 at 11:51 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> On 23 January 2013 15:06, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
>> On Wed, Jan 23, 2013 at 11:22 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:

>>> Second to solve your problem, you can add another field here: total_len.
>>> I know it will consume 4 bytes per desc but i think that's the drawback we need
>>> to accept.
>>
>> I found already better solution I guess.
>
> Wow!!
>
>> I introduced two functions to get amount of sent bytes like
>>
>> u32 calc_sent(u32 ctlhi, u32 ctllo)
>> {
>>  return f1(ctlhi) * f2(ctllo);
>> }
>>
>> u32 get_sent(dwc)
>> {
>>  return calc_sent(read(CTL_HI), read(CTL_LO));
>> }
>>
>> And usage like
>>
>> /* initial residue */
>> desc->len - calc_sent(desc->lli.ctlhi, desc->lli.ctllo).
>>
>> What do you think?
>
> You plan to use it for
> - the first descriptor in a list as others already have length embedded in them?
> - And the descriptor currently getting used, by reading its ctlhi/lo
> from registers
>   instead of lli.*** ?

Roughly, yes.

> Looks good. but still keeping len of individual descriptors in all
> descriptors leaving
> the first one is not the code i would like to keep :)

What about to calc len every time from lli.* instead of keeping it in
the len field of the descriptor?
It's logically looks better, but requires more resources.

-- 
With Best Regards,
Andy Shevchenko
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