Re: [PATCH 15/27] ALSA: hda - Use timecounter_initialize interface - Pierre-Louis Bossart

From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: Sagar Arun Kamble <sagar.a.kamble@intel.com>,
	Richard Cochran <richardcochran@gmail.com>
Cc: Takashi Iwai <tiwai@suse.de>, Vinod Koul <vinod.koul@intel.com>,
	alsa-devel@alsa-project.org, Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 15/27] ALSA: hda - Use timecounter_initialize interface
Date: Tue, 2 Jan 2018 11:15:45 -0600	[thread overview]
Message-ID: <3c5734a2-8f97-4a8b-26d4-42852cc86352@linux.intel.com> (raw)
In-Reply-To: <1a9a1507-7ca3-459b-c2ce-02fc2afad2ff@intel.com>

On 1/2/18 12:03 AM, Sagar Arun Kamble wrote:
> 
> 
> On 12/28/2017 10:19 PM, Richard Cochran wrote:
>> On Tue, Dec 26, 2017 at 01:07:35PM +0530, Sagar Arun Kamble wrote:
>>>> Or can we provide simpler versions for covering some defaults?  At
>>>> least reducing the number of arguments would make things easier.
>>> Thought about specifying 1. cyclecounter read func 2. frequency 3. 
>>> width of
>>> counter as parameters here
>>> which can get rid of mult, shift params. But this is not easy as most 
>>> of the
>>> drivers do not specify
>>> cyclecounter frequency and instead hard-code the mult/shift factors.
>> You are talking about using clocks_calc_mult_shift() here, right? (See
>> the usage example in drivers/net/ethernet/ti/cpts.c).
> Yes
>> This is a good idea, and it is worth getting the driver authors' input
>> to figure out the correct parameters.

I wrote the code for HDaudio and I remember wasting time trying to 
figure out the gory details of the cycle counter stuff when all I wanted 
was a conversion from a 24MHz counter to ns values using a 125/3 
operation in the right order - as explained in the comments

If there was a helper to set those mult/shift values it'd make the 
HDaudio code clearer (and also help support newer modes of operation 
with a 12 and 6 MHz MCLK).

The initial proposal with hard-coded values in arguments instead of 
structure members didn't really make the code clearer.

>>
>> I bet we can use that almost everywhere.  If there are any drivers
>> that cannot be converted, then we can leave some sort of low level
>> legacy initialization method.
> Agree
>> Thanks,
>> Richard
>>
> 
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