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

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Date:	Wed, 20 Feb 2013 13:11:12 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Laxman Dewangan <ldewangan@...dia.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 Wed, Feb 20, 2013 at 05:59:03PM +0530, Laxman Dewangan wrote:
> On Tuesday 19 February 2013 11:46 PM, Stephen Warren wrote:

> >In the older Tegra SPI drivers, the PM runtime logic was was of
> >master->{un,}prepare_transfer. I'm curious why it's implemented
> >differently here.

> The prepare  is called in atomic context and in this we are calling
> pm_runtime_get_sync() which is blocking and it can cause issue.

> I have already bug reported by you that sometimes you saw locking in
> tegra20 slink driver which we need to fix. When testing this, I ran
> into similar case and hence now moving this out or prepare.

> I will push the change for fixing this in tegra20_slink driver also.

As I think I've said before I keep thinking we ought to just have some
basic runtime PM code in the core - a substantial proportion of drivers
end up following the same pattern, it'd be surprising to see hardware
that needed a different pattern.

> >>+	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.

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