Re: [PATCH v2 6/7] spi: s3c64xx: restore removed comments

From: Michael Turquette <mturquette-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>
To: Sylwester Nawrocki
	<s.nawrocki-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	Andi Shyti <andi.shyti-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Kukjin Kim <kgene-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Krzysztof Kozlowski
	<k.kozlowski-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Tomasz Figa <tomasz.figa-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Stephen Boyd <sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>,
	Chanwoo Choi <cw00.choi-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	Jaehoon Chung
	<jh80.chung-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Andi Shyti <andi-ahk0KpmfxKRAfugRpC6u6w@public.gmane.org>
Subject: Re: [PATCH v2 6/7] spi: s3c64xx: restore removed comments
Date: Mon, 11 Jul 2016 15:17:31 -0700	[thread overview]
Message-ID: <146827545163.73491.5083923656346798965@resonance> (raw)
In-Reply-To: <57837606.8050906-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>

Quoting Sylwester Nawrocki (2016-07-11 03:33:42)
> On 07/08/2016 06:17 PM, Michael Turquette wrote:
> > Quoting Andi Shyti (2016-07-08 07:46:40)
> 
> >> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
> >> index 6da663f..32b66f0 100644
> >> --- a/drivers/spi/spi-s3c64xx.c
> >> +++ b/drivers/spi/spi-s3c64xx.c
> >> @@ -639,6 +639,7 @@ static void s3c64xx_spi_config(struct s3c64xx_spi_driver_data *sdd)
> >>         writel(val, regs + S3C64XX_SPI_MODE_CFG);
> >>  
> >>         if (sdd->port_conf->clk_from_cmu) {
> >> +               /* There is half-multiplier before the SPI */
> >>                 clk_set_rate(sdd->src_clk, sdd->cur_speed * 2);
> > 
> > Just a small comment, but if the fixed-factor divide-by-two clock was
> > modeled in Linux, then this driver could call clk_set_rate on that clock
> > with the "correct" rate.
> > 
> > I guess that this driver would be the provider of that clock?
> 
> Good point, however I'm not sure if it is worth to model this divider
> with a clk object.  It is an internal divider and the clock it provides
> is only used internally within the SPI controller.  Thus the spi-s3c64xx
> driver would be provider on the only consumer of this clock.

Sure, but it's only a few lines of code to this, and there are examples
in the kernel already.

> 
> Additionally, the "There is half-multiplier before the SPI" comment
> seems to be obfuscating how the hardware really looks like to me.
> It talks about multiplier (which reminds me of PLLs with a divider
> in the feedback loop) while there is a simple divider which should
> be considered as an integral part of the controller IP block.
> 
> While we are at it, I'd propose to change this comment to something
> like:
> 
> /* The SCLK_SPI clock is divided internally by 2 */

It's your choice, but debug output would benefit from showing the real
clock frequency at some point.

Regards,
Mike
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