linux-kernel - Re: [PATCH] spi: tegra114: add spi driver

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Date:	Thu, 21 Feb 2013 11:56:54 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Laxman Dewangan <ldewangan@...dia.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH] spi: tegra114: add spi driver

On Wed, Feb 20, 2013 at 06:25:13PM +0100, Stephen Warren wrote:
> On 02/20/2013 06:26 AM, Laxman Dewangan wrote:
> > On Wednesday 20 February 2013 06:41 PM, Mark Brown wrote:
> >> * PGP Signed by an unknown key
> >>
> >> On Wed, Feb 20, 2013 at 05:59:03PM +0530, Laxman Dewangan wrote:
> >>>>> +    tspi->clk = devm_clk_get(&pdev->dev, "spi");
> >>>> Does this HW block use multiple clocks? If not, I think s/"spi"/NULL/
> >>>> there, just like the Tegra20 driver.
> >>> No, spi controller uses the only one clock. I will change to NULL.
> >> I'm never convinced that NULL is a helpful clock name to pick, it's not
> >> awesome if you ever acquire a second clock.
> > 
> > I had other idea of okeeping clock name here for power optimization.
> > Spi controller can take the power source ffrom different clock source
> > say clk_m (crystal) and pllp.
> > 
> > I want to set the parent clock dynamically based on required speed so
> > that if the desire speed can be meet from clk_m, no need to increase pll
> > count and possible we may endup with siwtchng off pllp which can save
> > power.
> > 
> > So for this I may require
> > 
> > spi_clk = devm_clk_get(&pdev->dev, "spi");
> > spi_clkm = devm_clk_get(&pdev->dev, "clmkm");
> > spi_pllp = devm_clk_get(&pdev->dev, "pllp");
> > 
> > and call clk_set_parent(spi_clk, spi_clkm) or clk_set_parent(spi_clk,
> > spi_pllp).
> 
> OK, so that's certainly an argument for requesting a specific clock name
> rather than NULL.
> 

The list of possible parents for each clock is determined by the SoC and is
already known to CCF, so maybe we just need to add a function to CCF to allow
the drivers to query the list of possible parents?

Cheers,

Peter.
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