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

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Date:	Wed, 20 Feb 2013 18:56:13 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	Stephen Warren <swarren@...dotorg.org>,
	"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 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).







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