diff mbox series

[v3,54/65] clk: da8xx: clk48: Switch to determine_rate

Message ID 20221018-clk-range-checks-fixes-v3-54-9a1358472d52@cerno.tech (mailing list archive)
State New, archived
Headers show
Series clk: Make determine_rate mandatory for muxes | expand

Commit Message

Maxime Ripard April 4, 2023, 10:11 a.m. UTC
The TI DA8xx USB0 clk48 clocks implements a mux with a set_parent
hook, but doesn't provide a determine_rate implementation.

This is a bit odd, since set_parent() is there to, as its name implies,
change the parent of a clock. However, the most likely candidate to
trigger that parent change is a call to clk_set_rate(), with
determine_rate() figuring out which parent is the best suited for a
given rate.

The other trigger would be a call to clk_set_parent(), but it's far less
used, and it doesn't look like there's any obvious user for that clock.

So, the set_parent hook is effectively unused, possibly because of an
oversight. However, it could also be an explicit decision by the
original author to avoid any reparenting but through an explicit call to
clk_set_parent().

The driver does implement round_rate() though, which means that we can
change the rate of the clock, but we will never get to change the
parent.

However, It's hard to tell whether it's been done on purpose or not.

Since we'll start mandating a determine_rate() implementation, let's
convert the round_rate() implementation to a determine_rate(), which
will also make the current behavior explicit. And if it was an
oversight, the clock behaviour can be adjusted later on.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/clk/davinci/da8xx-cfgchip.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Comments

David Lechner April 5, 2023, 3:03 p.m. UTC | #1
On 4/4/23 5:11 AM, Maxime Ripard wrote:
> The TI DA8xx USB0 clk48 clocks implements a mux with a set_parent
> hook, but doesn't provide a determine_rate implementation.
> 
> This is a bit odd, since set_parent() is there to, as its name implies,
> change the parent of a clock. However, the most likely candidate to
> trigger that parent change is a call to clk_set_rate(), with
> determine_rate() figuring out which parent is the best suited for a
> given rate.
> 

As mentioned in my previous review, parent is selected by device
tree and should never be changed after init.
Maxime Ripard April 5, 2023, 3:22 p.m. UTC | #2
Hi David,

On Wed, Apr 05, 2023 at 10:03:24AM -0500, David Lechner wrote:
> On 4/4/23 5:11 AM, Maxime Ripard wrote:
> > The TI DA8xx USB0 clk48 clocks implements a mux with a set_parent
> > hook, but doesn't provide a determine_rate implementation.
> > 
> > This is a bit odd, since set_parent() is there to, as its name implies,
> > change the parent of a clock. However, the most likely candidate to
> > trigger that parent change is a call to clk_set_rate(), with
> > determine_rate() figuring out which parent is the best suited for a
> > given rate.
> > 
> 
> As mentioned in my previous review, parent is selected by device
> tree and should never be changed after init.

Great minds think alike then, because the driver implements exactly
that, either before or after that patch.

That patch makes the current behaviour explicit but doesn't change it in
any way.

So I guess that means that I can add your Acked-by on the three patches
you reviewed with the same message?

Maxime
David Lechner April 5, 2023, 4:07 p.m. UTC | #3
On 4/5/23 10:22 AM, Maxime Ripard wrote:
> Hi David,
> 
> On Wed, Apr 05, 2023 at 10:03:24AM -0500, David Lechner wrote:
>> On 4/4/23 5:11 AM, Maxime Ripard wrote:
>>> The TI DA8xx USB0 clk48 clocks implements a mux with a set_parent
>>> hook, but doesn't provide a determine_rate implementation.
>>>
>>> This is a bit odd, since set_parent() is there to, as its name implies,
>>> change the parent of a clock. However, the most likely candidate to
>>> trigger that parent change is a call to clk_set_rate(), with
>>> determine_rate() figuring out which parent is the best suited for a
>>> given rate.
>>>
>>
>> As mentioned in my previous review, parent is selected by device
>> tree and should never be changed after init.
> 
> Great minds think alike then, because the driver implements exactly
> that, either before or after that patch.
> 
> That patch makes the current behaviour explicit but doesn't change it in
> any way.
> 
> So I guess that means that I can add your Acked-by on the three patches
> you reviewed with the same message?
> 
> Maxime

Yes, preferably with a simplified commit message.

Acked-by: David Lechner <david@lechnology.com>
diff mbox series

Patch

diff --git a/drivers/clk/davinci/da8xx-cfgchip.c b/drivers/clk/davinci/da8xx-cfgchip.c
index 4c1cc59bba53..f60c97091818 100644
--- a/drivers/clk/davinci/da8xx-cfgchip.c
+++ b/drivers/clk/davinci/da8xx-cfgchip.c
@@ -462,10 +462,12 @@  static unsigned long da8xx_usb0_clk48_recalc_rate(struct clk_hw *hw,
 	return 48000000;
 }
 
-static long da8xx_usb0_clk48_round_rate(struct clk_hw *hw, unsigned long rate,
-					unsigned long *parent_rate)
+static int da8xx_usb0_clk48_determine_rate(struct clk_hw *hw,
+					   struct clk_rate_request *req)
 {
-	return 48000000;
+	req->rate = 48000000;
+
+	return 0;
 }
 
 static int da8xx_usb0_clk48_set_parent(struct clk_hw *hw, u8 index)
@@ -494,7 +496,7 @@  static const struct clk_ops da8xx_usb0_clk48_ops = {
 	.disable	= da8xx_usb0_clk48_disable,
 	.is_enabled	= da8xx_usb0_clk48_is_enabled,
 	.recalc_rate	= da8xx_usb0_clk48_recalc_rate,
-	.round_rate	= da8xx_usb0_clk48_round_rate,
+	.determine_rate	= da8xx_usb0_clk48_determine_rate,
 	.set_parent	= da8xx_usb0_clk48_set_parent,
 	.get_parent	= da8xx_usb0_clk48_get_parent,
 };