Re: [PATCH] spi: tegra114: add spi driver

[Peter De Schrijver <pdeschrijver@nvidia.com>]

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.