linux-kernel - RE: [PATCH v2 0/2] soundwire: set frame shape and divider based on actual clk

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Message-ID: <SJ2PR11MB8424ACAB4FD02EABC57FFF16FFE72@SJ2PR11MB8424.namprd11.prod.outlook.com>
Date: Mon, 20 Jan 2025 02:06:07 +0000
From: "Liao, Bard" <bard.liao@...el.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>, Bard Liao
	<yung-chuan.liao@...ux.intel.com>, "linux-sound@...r.kernel.org"
	<linux-sound@...r.kernel.org>, "vkoul@...nel.org" <vkoul@...nel.org>
CC: "vinod.koul@...aro.org" <vinod.koul@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 0/2] soundwire: set frame shape and divider based on
 actual clk



> -----Original Message-----
> From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
> Sent: Saturday, January 18, 2025 12:11 AM
> To: Bard Liao <yung-chuan.liao@...ux.intel.com>; linux-sound@...r.kernel.org;
> vkoul@...nel.org
> Cc: vinod.koul@...aro.org; linux-kernel@...r.kernel.org; Liao, Bard
> <bard.liao@...el.com>
> Subject: Re: [PATCH v2 0/2] soundwire: set frame shape and divider based on
> actual clk
> 
> On 1/14/25 12:16 AM, Bard Liao wrote:
> > Set frame shape and clock divider based on actual clock frequency. And
> > with that change, we can support ckock change in Intel platforms.
> >
> > v2:
> >  - Mave the check before writing the divider registers
> >  - Remove the 'freq' intermediate variable which is multiplied by two
> >    after divided by two.
> >
> > Bard Liao (2):
> >   soundwire: cadence_master: set frame shape and divider based on actual
> >     clk freq
> >   Revert "soundwire: intel_auxdevice: start the bus at default
> >     frequency"
> 
> This looks fine so
> 
> Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
> 
> but one additional question: what is the default start frequency? There is an
> expectation in SoundWire 1.2 that the bus starts at the slowest speed to allow
> for potential programming of PHY registers before bumping the speed to a
> higher rate. I don't recall what is typically listed in the _DSD properties, it'd be a
> mistake to start blindly with the first listed value if it happens to be the max
> rate.

Currently, we start with the first listed value. I checked the listed
values, and the first value is the slowest and the latter is faster.
But, yes, I agree that we can't rely on the _DSD properties.
Let's sort it when we get the values.

> 
> >  drivers/soundwire/cadence_master.c  | 22 +++++++++++++++++++---
> >  drivers/soundwire/intel_auxdevice.c | 21 ---------------------
> >  2 files changed, 19 insertions(+), 24 deletions(-)
> >