arc: get rate from clk driver instead of reading device tree

Submitted by Zakharov Vlad on Feb. 22, 2017, 10:36 a.m.

Details

Message ID 1487759796-14418-1-git-send-email-vzakhar@synopsys.com
State New
Headers show

Commit Message

Zakharov Vlad Feb. 22, 2017, 10:36 a.m.
We were reading clock rate directly from device tree "clock-frequency"
property of corresponding clock node in show_cpuinfo function.

Such approach is correct only in case cpu is always clocked by
"fixed-clock". If we use clock driver that allows rate to be changed
this won't work as rate may change during the time or even
"clock-frequency" property may not be presented at all.

So this commit replaces reading device tree with getting rate from clock
driver. This approach is much more flexible and will work for both fixed
and mutable clocks.

Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
---
 arch/arc/kernel/setup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Vineet Gupta Feb. 22, 2017, 6:34 p.m.
On 02/22/2017 02:36 AM, Vlad Zakharov wrote:
> We were reading clock rate directly from device tree "clock-frequency"
> property of corresponding clock node in show_cpuinfo function.
> 
> Such approach is correct only in case cpu is always clocked by
> "fixed-clock". If we use clock driver that allows rate to be changed
> this won't work as rate may change during the time or even
> "clock-frequency" property may not be presented at all.
> 
> So this commit replaces reading device tree with getting rate from clock
> driver. This approach is much more flexible and will work for both fixed
> and mutable clocks.
> 
> Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
> ---
>  arch/arc/kernel/setup.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
> index 3093fa8..49b0804 100644
> --- a/arch/arc/kernel/setup.c
> +++ b/arch/arc/kernel/setup.c
> @@ -10,6 +10,7 @@
>  #include <linux/fs.h>
>  #include <linux/delay.h>
>  #include <linux/root_dev.h>
> +#include <linux/clk.h>
>  #include <linux/clk-provider.h>
>  #include <linux/clocksource.h>
>  #include <linux/console.h>
> @@ -488,7 +489,8 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  {
>  	char *str;
>  	int cpu_id = ptr_to_cpu(v);
> -	struct device_node *core_clk = of_find_node_by_name(NULL, "core_clk");
> +	struct device *cpu_dev = get_cpu_device(cpu_id);
> +	struct clk *cpu_clk = clk_get(cpu_dev, "core_clk");
>  	u32 freq = 0;
>  
>  	if (!cpu_online(cpu_id)) {
> @@ -502,7 +504,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  
>  	seq_printf(m, arc_cpu_mumbojumbo(cpu_id, str, PAGE_SIZE));
>  
> -	of_property_read_u32(core_clk, "clock-frequency", &freq);
> +	freq = clk_get_rate(cpu_clk);
>  	if (freq)
>  		seq_printf(m, "CPU speed\t: %u.%02u Mhz\n",
>  			   freq / 1000000, (freq / 10000) % 100);

I'm not too familiar with clk API, do u need to clk_put() afterwards ? @Alexey can
u please check !
Vineet Gupta Feb. 22, 2017, 6:49 p.m.
On 02/22/2017 02:36 AM, Vlad Zakharov wrote:
> We were reading clock rate directly from device tree "clock-frequency"
> property of corresponding clock node in show_cpuinfo function.
> 
> Such approach is correct only in case cpu is always clocked by
> "fixed-clock". If we use clock driver that allows rate to be changed
> this won't work as rate may change during the time or even
> "clock-frequency" property may not be presented at all.
> 
> So this commit replaces reading device tree with getting rate from clock
> driver. This approach is much more flexible and will work for both fixed
> and mutable clocks.

So except the clk_put() comment - this looks much better to me.

And while we are at it - one of my wish list has been to print the core clk in
early boot - i.e. in setup_processor()->arc_cpu_mumbojumbo() call path which is
different from the other case u fixed. Any ideas how to do that - clk framework
will not have init by then - so we need to read out from FDT or some such !

> 
> Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>
> ---
>  arch/arc/kernel/setup.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
> index 3093fa8..49b0804 100644
> --- a/arch/arc/kernel/setup.c
> +++ b/arch/arc/kernel/setup.c
> @@ -10,6 +10,7 @@
>  #include <linux/fs.h>
>  #include <linux/delay.h>
>  #include <linux/root_dev.h>
> +#include <linux/clk.h>
>  #include <linux/clk-provider.h>
>  #include <linux/clocksource.h>
>  #include <linux/console.h>
> @@ -488,7 +489,8 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  {
>  	char *str;
>  	int cpu_id = ptr_to_cpu(v);
> -	struct device_node *core_clk = of_find_node_by_name(NULL, "core_clk");
> +	struct device *cpu_dev = get_cpu_device(cpu_id);
> +	struct clk *cpu_clk = clk_get(cpu_dev, "core_clk");
>  	u32 freq = 0;
>  
>  	if (!cpu_online(cpu_id)) {
> @@ -502,7 +504,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>  
>  	seq_printf(m, arc_cpu_mumbojumbo(cpu_id, str, PAGE_SIZE));
>  
> -	of_property_read_u32(core_clk, "clock-frequency", &freq);
> +	freq = clk_get_rate(cpu_clk);
>  	if (freq)
>  		seq_printf(m, "CPU speed\t: %u.%02u Mhz\n",
>  			   freq / 1000000, (freq / 10000) % 100);
>
Alexey Brodkin Feb. 28, 2017, 3:11 p.m.
Hi Vineet,

On Wed, 2017-02-22 at 10:34 -0800, Vineet Gupta wrote:
> On 02/22/2017 02:36 AM, Vlad Zakharov wrote:

> > 

> > We were reading clock rate directly from device tree "clock-frequency"

> > property of corresponding clock node in show_cpuinfo function.

> > 

> > Such approach is correct only in case cpu is always clocked by

> > "fixed-clock". If we use clock driver that allows rate to be changed

> > this won't work as rate may change during the time or even

> > "clock-frequency" property may not be presented at all.

> > 

> > So this commit replaces reading device tree with getting rate from clock

> > driver. This approach is much more flexible and will work for both fixed

> > and mutable clocks.

> > 

> > Signed-off-by: Vlad Zakharov <vzakhar@synopsys.com>

> > ---

> >  arch/arc/kernel/setup.c | 6 ++++--

> >  1 file changed, 4 insertions(+), 2 deletions(-)

> > 

> > diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c

> > index 3093fa8..49b0804 100644

> > --- a/arch/arc/kernel/setup.c

> > +++ b/arch/arc/kernel/setup.c

> > @@ -10,6 +10,7 @@

> >  #include <linux/fs.h>

> >  #include <linux/delay.h>

> >  #include <linux/root_dev.h>

> > +#include <linux/clk.h>

> >  #include <linux/clk-provider.h>

> >  #include <linux/clocksource.h>

> >  #include <linux/console.h>

> > @@ -488,7 +489,8 @@ static int show_cpuinfo(struct seq_file *m, void *v)

> >  {

> >  	char *str;

> >  	int cpu_id = ptr_to_cpu(v);

> > -	struct device_node *core_clk = of_find_node_by_name(NULL, "core_clk");

> > +	struct device *cpu_dev = get_cpu_device(cpu_id);

> > +	struct clk *cpu_clk = clk_get(cpu_dev, "core_clk");

> >  	u32 freq = 0;

> >  

> >  	if (!cpu_online(cpu_id)) {

> > @@ -502,7 +504,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)

> >  

> >  	seq_printf(m, arc_cpu_mumbojumbo(cpu_id, str, PAGE_SIZE));

> >  

> > -	of_property_read_u32(core_clk, "clock-frequency", &freq);

> > +	freq = clk_get_rate(cpu_clk);

> >  	if (freq)

> >  		seq_printf(m, "CPU speed\t: %u.%02u Mhz\n",

> >  			   freq / 1000000, (freq / 10000) % 100);

> 

> I'm not too familiar with clk API, do u need to clk_put() afterwards ? @Alexey can

> u please check !


I'm not really sure why clk_put() got in the picture here at all.
As it is mentioned here http://elixir.free-electrons.com/source/include/linux/clk.h?v=4.10#L305
clk_put() means "free" the clock source.

Anyways this patch alone was not sufficient due to missing changes in .dts files and
Vlad is going to send v2 soonish.

-Alexey
Zakharov Vlad March 9, 2017, 7:33 p.m.
Hi Vineet,

On Wed, 2017-02-22 at 10:49 -0800, Vineet Gupta wrote:
> On 02/22/2017 02:36 AM, Vlad Zakharov wrote:

> > We were reading clock rate directly from device tree "clock-frequency"

> > property of corresponding clock node in show_cpuinfo function.

> > 

> > Such approach is correct only in case cpu is always clocked by

> > "fixed-clock". If we use clock driver that allows rate to be changed

> > this won't work as rate may change during the time or even

> > "clock-frequency" property may not be presented at all.

> > 

> > So this commit replaces reading device tree with getting rate from clock

> > driver. This approach is much more flexible and will work for both fixed

> > and mutable clocks.

> 

> So except the clk_put() comment - this looks much better to me.

> 

> And while we are at it - one of my wish list has been to print the core clk in

> early boot - i.e. in setup_processor()->arc_cpu_mumbojumbo() call path which is

> different from the other case u fixed. Any ideas how to do that - clk framework

> will not have init by then - so we need to read out from FDT or some such !


We can either parse FDT or read from real hardware - but is that the point?
I thought the goal is to get rid of as much board-dependent code as possible, isn't it?

In fact there are two ways of getting frequencies before clk framework inits: 

  1) Parse FDT - this way is not platform-dependent, but if someone adds clock nodes without "clock-frequency" property
this is gonna fail. The second issue here is that device tree property is not believed to be accurate - actual value may
differ. So, there are a lot of disadvantages.

  2) Read values from real hardware: this is platform-dependent way and we will have add such "hacks" for each supported
platform even if clock driver is provided for such platform. And that's why I don't like this way.

Of course clk framework initializes a bit later. But maybe we can wait for this and add just a couple of code lines that
read rate using common clk API?

-- 
Best regards,
Vlad Zakharov <vzakhar@synopsys.com>
Vineet Gupta March 10, 2017, 1:24 a.m.
On 03/09/2017 11:33 AM, Vlad Zakharov wrote:
>
>> And while we are at it - one of my wish list has been to print the core clk in
>> early boot - i.e. in setup_processor()->arc_cpu_mumbojumbo() call path which is
>> different from the other case u fixed. Any ideas how to do that - clk framework
>> will not have init by then - so we need to read out from FDT or some such !
> We can either parse FDT or read from real hardware - but is that the point?
> I thought the goal is to get rid of as much board-dependent code as possible, isn't it?

I'm not asking to add board specific code in setup.c - but we do want to print the
frequency as available. Currently we only print for AXS but for some new board it
will likely not be present so at the very least print what is in the DT.

So the idea would be to have a default which reads from FDT and board/platform can
override it with more accurate info (from say hardware). You can start off with
using weak function approach for prototyping and later use a callback approach
registered by boards etc !

> In fact there are two ways of getting frequencies before clk framework inits: 
>
>   1) Parse FDT - this way is not platform-dependent, but if someone adds clock nodes without "clock-frequency" property
> this is gonna fail. The second issue here is that device tree property is not believed to be accurate - actual value may
> differ. So, there are a lot of disadvantages.
>
>   2) Read values from real hardware: this is platform-dependent way and we will have add such "hacks" for each supported
> platform even if clock driver is provided for such platform. And that's why I don't like this way.
>
> Of course clk framework initializes a bit later. But maybe we can wait for this and add just a couple of code lines that
> read rate using common clk API?

I'd still prefer to see the value provided in DT and any updates since !

-Vineet
-Vineet

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diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
index 3093fa8..49b0804 100644
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -10,6 +10,7 @@ 
 #include <linux/fs.h>
 #include <linux/delay.h>
 #include <linux/root_dev.h>
+#include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/clocksource.h>
 #include <linux/console.h>
@@ -488,7 +489,8 @@  static int show_cpuinfo(struct seq_file *m, void *v)
 {
 	char *str;
 	int cpu_id = ptr_to_cpu(v);
-	struct device_node *core_clk = of_find_node_by_name(NULL, "core_clk");
+	struct device *cpu_dev = get_cpu_device(cpu_id);
+	struct clk *cpu_clk = clk_get(cpu_dev, "core_clk");
 	u32 freq = 0;
 
 	if (!cpu_online(cpu_id)) {
@@ -502,7 +504,7 @@  static int show_cpuinfo(struct seq_file *m, void *v)
 
 	seq_printf(m, arc_cpu_mumbojumbo(cpu_id, str, PAGE_SIZE));
 
-	of_property_read_u32(core_clk, "clock-frequency", &freq);
+	freq = clk_get_rate(cpu_clk);
 	if (freq)
 		seq_printf(m, "CPU speed\t: %u.%02u Mhz\n",
 			   freq / 1000000, (freq / 10000) % 100);