linux-kernel - Re: [PATCH 1/2] ARM: tegra: Add Tegra20 host1x support

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Message-ID: <20121113064135.GA31443@avionic-0098.mockup.avionic-design.de>
Date:	Tue, 13 Nov 2012 07:41:36 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Mark Zhang <markz@...dia.com>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ARM: tegra: Add Tegra20 host1x support

On Tue, Nov 13, 2012 at 12:38:34PM +0800, Mark Zhang wrote:
> On 11/12/2012 05:39 PM, Mark Zhang wrote:
> > On 11/09/2012 09:20 PM, Thierry Reding wrote:
[...]
> >> @@ -1036,9 +1041,6 @@ static struct clk_duplicate tegra_clk_duplicates[] = {
> >>         CLK_DUPLICATE("usbd",   "utmip-pad",    NULL),
> >>         CLK_DUPLICATE("usbd",   "tegra-ehci.0", NULL),
> >>         CLK_DUPLICATE("usbd",   "tegra-otg",    NULL),
> >> -       CLK_DUPLICATE("hdmi",   "tegradc.0",    "hdmi"),
> >> -       CLK_DUPLICATE("hdmi",   "tegradc.1",    "hdmi"),
> >> -       CLK_DUPLICATE("host1x", "tegra_grhost", "host1x"),
> >>         CLK_DUPLICATE("2d",     "tegra_grhost", "gr2d"),
> >>         CLK_DUPLICATE("3d",     "tegra_grhost", "gr3d"),
> >>         CLK_DUPLICATE("epp",    "tegra_grhost", "epp"),
> >> @@ -1051,6 +1053,9 @@ static struct clk_duplicate tegra_clk_duplicates[] = {
> >>         CLK_DUPLICATE("pll_p_out3", "tegra-i2c.1", "fast-clk"),
> >>         CLK_DUPLICATE("pll_p_out3", "tegra-i2c.2", "fast-clk"),
> >>         CLK_DUPLICATE("pll_p_out3", "tegra-i2c.3", "fast-clk"),
> >> +       CLK_DUPLICATE("pll_p", "tegra-dc.0", "parent"),
> >> +       CLK_DUPLICATE("pll_p", "tegra-dc.1", "parent"),
> >> +       CLK_DUPLICATE("pll_d_out0", "tegra-hdmi", "parent"),
> >>  };
> 
> Why we need this "CLK_DUPLICATE"? Set the clock parent of the dc
> controllers to pll_p?

This was the method proposed by Stephen to abstract away the clock tree
differences between Tegra20 and Tegra30. The way this works is that we
can {devm_,}clk_get(&pdev->dev, "parent") in the display and HDMI
controllers' .probe() and it'll obtain the correct parent clock
independent of which version of Tegra is used.

Thierry

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