Re: [PATCH v13 3/6] clk: Make clk API return per-user struct clk instances

[Stephen Boyd <sboyd@codeaurora.org>]

On 02/06/15 05:39, Russell King - ARM Linux wrote:
> On Thu, Feb 05, 2015 at 05:35:28PM -0800, Stephen Boyd wrote:
>
>> From what I can tell this code is
>> now broken because we made all clk getting functions (there's quite a
>> few...) return unique pointers every time they're called. It seems that
>> the driver wants to know if extclk and clk are the same so it can do
>> something differently in kirkwood_set_rate(). Do we need some sort of
>> clk_equal(struct clk *a, struct clk *b) function for drivers like this?
> Well, the clocks in question are the SoC internal clock (which is more or
> less fixed, but has a programmable divider) and an externally supplied
> clock, and the IP has a multiplexer on its input which allows us to select
> between those two sources.
>
> If it were possible to bind both to the same clock, it wouldn't be a
> useful configuration - nothing would be gained from doing so in terms of
> available rates.
>
> What the comparison is there for is to catch the case with legacy lookups
> where a clkdev lookup entry with a NULL connection ID results in matching
> any connection ID passed to clk_get().  If the patch changes this, then
> we will have a regression - and this is something which needs fixing
> _before_ we do this "return unique clocks".
>

Ok. It seems that we might need a clk_equal() or similar API after all.
My understanding is that this driver is calling clk_get() twice with
NULL for the con_id and then "extclk" in attempts to get the SoC
internal clock and the externally supplied clock. If we're using legacy
lookups then both clk_get() calls may map to the same clk_lookup entry
and before Tomeu's patch that returns unique clocks the driver could
detect this case and know that there isn't an external clock. Looking at
arch/arm/mach-dove/common.c it seems that there is only one lookup per
device and it has a wildcard NULL for con_id so both clk_get() calls
here are going to find the same lookup and get a unique struct clk pointer.

Why don't we make the legacy lookup more specific and actually indicate
"internal" for the con_id? Then the external clock would fail to be
found, but we can detect that case and figure out that it's not due to
probe defer, but instead due to the fact that there really isn't any
mapping. It looks like the code is already prepared for this anyway.

----8<----

From: Stephen Boyd <sboyd@codeaurora.org>
Subject: [PATCH] ARM: dove: Remove wildcard from mvebu-audio device clk lookup

This i2s driver is using the wildcard nature of clkdev lookups to
figure out if there's an external clock or not. It does this by
calling clk_get() twice with NULL for the con_id first and then
"external" for the con_id the second time around and then
compares the two pointers. With DT the wildcard feature of
clk_get() is gone and so the driver has to handle an error from
the second clk_get() call as meaning "no external clock
specified". Let's use that logic even with clk lookups to
simplify the code and remove the struct clk pointer comparisons
which may not work in the future when clk_get() returns unique
pointers.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 arch/arm/mach-dove/common.c       |  4 ++--
 sound/soc/kirkwood/kirkwood-i2s.c | 13 ++++---------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/arm/mach-dove/common.c b/arch/arm/mach-dove/common.c
index 0d1a89298ece..f290fc944cc1 100644
--- a/arch/arm/mach-dove/common.c
+++ b/arch/arm/mach-dove/common.c
@@ -124,8 +124,8 @@ static void __init dove_clk_init(void)
 	orion_clkdev_add(NULL, "sdhci-dove.1", sdio1);
 	orion_clkdev_add(NULL, "orion_nand", nand);
 	orion_clkdev_add(NULL, "cafe1000-ccic.0", camera);
-	orion_clkdev_add(NULL, "mvebu-audio.0", i2s0);
-	orion_clkdev_add(NULL, "mvebu-audio.1", i2s1);
+	orion_clkdev_add("internal", "mvebu-audio.0", i2s0);
+	orion_clkdev_add("internal", "mvebu-audio.1", i2s1);
 	orion_clkdev_add(NULL, "mv_crypto", crypto);
 	orion_clkdev_add(NULL, "dove-ac97", ac97);
 	orion_clkdev_add(NULL, "dove-pdma", pdma);
diff --git a/sound/soc/kirkwood/kirkwood-i2s.c b/sound/soc/kirkwood/kirkwood-i2s.c
index def7d8260c4e..0bfeb712a997 100644
--- a/sound/soc/kirkwood/kirkwood-i2s.c
+++ b/sound/soc/kirkwood/kirkwood-i2s.c
@@ -564,7 +564,7 @@ static int kirkwood_i2s_dev_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	priv->clk = devm_clk_get(&pdev->dev, np ? "internal" : NULL);
+	priv->clk = devm_clk_get(&pdev->dev, "internal");
 	if (IS_ERR(priv->clk)) {
 		dev_err(&pdev->dev, "no clock\n");
 		return PTR_ERR(priv->clk);
@@ -579,14 +579,9 @@ static int kirkwood_i2s_dev_probe(struct platform_device *pdev)
 		if (PTR_ERR(priv->extclk) == -EPROBE_DEFER)
 			return -EPROBE_DEFER;
 	} else {
-		if (priv->extclk == priv->clk) {
-			devm_clk_put(&pdev->dev, priv->extclk);
-			priv->extclk = ERR_PTR(-EINVAL);
-		} else {
-			dev_info(&pdev->dev, "found external clock\n");
-			clk_prepare_enable(priv->extclk);
-			soc_dai = kirkwood_i2s_dai_extclk;
-		}
+		dev_info(&pdev->dev, "found external clock\n");
+		clk_prepare_enable(priv->extclk);
+		soc_dai = kirkwood_i2s_dai_extclk;
 	}
 
 	/* Some sensible defaults - this reflects the powerup values */

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