[PATCH] spi: bcm63xx-hsspi: Really keep pll clk enabled

[PATCH] spi: bcm63xx-hsspi: Really keep pll clk enabled

[Christophe JAILLET]

The purpose of commit 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
was to keep the pll clk enabled through the lifetime of the device.

In order to do that, some 'clk_prepare_enable()'/'clk_disable_unprepare()'
calls have been added in the error handling path of the probe function, in
the remove function and in the suspend and resume functions.

However, a 'clk_disable_unprepare()' call has been unfortunately left in
the probe function. So the commit seems to be more or less a no-op.

Axe it now, so that the pll clk is left enabled through the lifetime of
the device, as described in the commit.

Fixes: 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
To be honest, I don't see why we need to keep pll clk, or hsspi clk
enabled during the lifetime of the driver. My understanding of the code is
that it is only used to get the 'speed_hz' value in the probe function.
This value is never refreshed afterwards.
I don't see the point in enabling/disabling the clks. I think that they
both could be disabled in the probe function, without the need to keep
track in the bcm63xx_hsspi structure, neither during pm cycles or the
remove fucntion.

However, my knowledge on drivers is limited and I may be completly wrong :)
---
 drivers/spi/spi-bcm63xx-hsspi.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/spi/spi-bcm63xx-hsspi.c b/drivers/spi/spi-bcm63xx-hsspi.c
index 7327309ea3d5..6c235306c0e4 100644
--- a/drivers/spi/spi-bcm63xx-hsspi.c
+++ b/drivers/spi/spi-bcm63xx-hsspi.c
@@ -366,7 +366,6 @@ static int bcm63xx_hsspi_probe(struct platform_device *pdev)
 			goto out_disable_clk;
 
 		rate = clk_get_rate(pll_clk);
-		clk_disable_unprepare(pll_clk);
 		if (!rate) {
 			ret = -EINVAL;
 			goto out_disable_pll_clk;
-- 
2.20.1

Re: [PATCH] spi: bcm63xx-hsspi: Really keep pll clk enabled

[Mark Brown]

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On Fri, Feb 28, 2020 at 10:38:38PM +0100, Christophe JAILLET wrote:

> To be honest, I don't see why we need to keep pll clk, or hsspi clk
> enabled during the lifetime of the driver. My understanding of the code is
> that it is only used to get the 'speed_hz' value in the probe function.
> This value is never refreshed afterwards.
> I don't see the point in enabling/disabling the clks. I think that they
> both could be disabled in the probe function, without the need to keep
> track in the bcm63xx_hsspi structure, neither during pm cycles or the
> remove fucntion.

If the device has a clock there's a good chance it's needed for the
device to operate and that disabling it will save a little power when
the device isn't doing anything.

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Re: [PATCH] spi: bcm63xx-hsspi: Really keep pll clk enabled

[Jonas Gorski]

On Fri, 28 Feb 2020 at 22:38, Christophe JAILLET
<christophe.jaillet-39ZsbGIQGT5GWvitb5QawA@public.gmane.org> wrote:
>
> The purpose of commit 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
> was to keep the pll clk enabled through the lifetime of the device.
>
> In order to do that, some 'clk_prepare_enable()'/'clk_disable_unprepare()'
> calls have been added in the error handling path of the probe function, in
> the remove function and in the suspend and resume functions.
>
> However, a 'clk_disable_unprepare()' call has been unfortunately left in
> the probe function. So the commit seems to be more or less a no-op.
>
> Axe it now, so that the pll clk is left enabled through the lifetime of
> the device, as described in the commit.

Good catch!

Acked-by: Jonas Gorski <jonas.gorski-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

>
> Fixes: 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
> Signed-off-by: Christophe JAILLET <christophe.jaillet-39ZsbGIQGT5GWvitb5QawA@public.gmane.org>
> ---
> To be honest, I don't see why we need to keep pll clk, or hsspi clk
> enabled during the lifetime of the driver. My understanding of the code is
> that it is only used to get the 'speed_hz' value in the probe function.
> This value is never refreshed afterwards.
> I don't see the point in enabling/disabling the clks. I think that they
> both could be disabled in the probe function, without the need to keep
> track in the bcm63xx_hsspi structure, neither during pm cycles or the
> remove fucntion.

The hsspi clock is actually gated, so it needs to stay on during use.
The pll clock is only used to convey the rate, but is not gate-able.
These used to be the same (that's why it checks for the rate of the
hsspi clock first), but were split to make it easier to move to common
clock framework (since we can just use the generic gated and
fixed-rate clock implementations).

Incidentally these are AFAIK also two inputs, so it even happens to
match the hardware more closely.

Since the pll clock isn't gated, we don't need to keep it enabled - we
don't even need to enable it in theory, but IIRC the common clock
system will complain if you try to get the rate of a non-enabled
clock. And if we do enable it, then we can also just keep it enabled
over the lifetime of the device.

Regards
Jonas

Applied "spi: bcm63xx-hsspi: Really keep pll clk enabled" to the spi tree

[Mark Brown]

The patch

   spi: bcm63xx-hsspi: Really keep pll clk enabled

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 51bddd4501bc414b8b1e8f4d096b4a5304068169 Mon Sep 17 00:00:00 2001
From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Date: Fri, 28 Feb 2020 22:38:38 +0100
Subject: [PATCH] spi: bcm63xx-hsspi: Really keep pll clk enabled

The purpose of commit 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
was to keep the pll clk enabled through the lifetime of the device.

In order to do that, some 'clk_prepare_enable()'/'clk_disable_unprepare()'
calls have been added in the error handling path of the probe function, in
the remove function and in the suspend and resume functions.

However, a 'clk_disable_unprepare()' call has been unfortunately left in
the probe function. So the commit seems to be more or less a no-op.

Axe it now, so that the pll clk is left enabled through the lifetime of
the device, as described in the commit.

Fixes: 0fd85869c2a9 ("spi/bcm63xx-hsspi: keep pll clk enabled")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://lore.kernel.org/r/20200228213838.7124-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 drivers/spi/spi-bcm63xx-hsspi.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/spi/spi-bcm63xx-hsspi.c b/drivers/spi/spi-bcm63xx-hsspi.c
index 7327309ea3d5..6c235306c0e4 100644
--- a/drivers/spi/spi-bcm63xx-hsspi.c
+++ b/drivers/spi/spi-bcm63xx-hsspi.c
@@ -366,7 +366,6 @@ static int bcm63xx_hsspi_probe(struct platform_device *pdev)
 			goto out_disable_clk;
 
 		rate = clk_get_rate(pll_clk);
-		clk_disable_unprepare(pll_clk);
 		if (!rate) {
 			ret = -EINVAL;
 			goto out_disable_pll_clk;
-- 
2.20.1