What's the proper use of con_id in clkdev

What's the proper use of con_id in clkdev

[York Sun]

Michael and Stephen,

Can you help me to understand "#define MAX_CON_ID 16" in clkdev.c? I am trying
to use clk_get() to acquire the clock with its name. This fails when the clock
name is more than 15 characters. I traced it to this macro.

The reason of using clk_get() is I don't have device tree for my platform until
device tree overlay is officially supported. So I use clkdev_add() in the clock
driver.

So my issue is with the MAX_CON_ID. Is there a reason to limit it to 16?
Wouldn't it be better to use kstrdup() in vclkdev_alloc()?

York

Re: What's the proper use of con_id in clkdev

[Stephen Boyd]

On 10/05, York Sun wrote:
> Michael and Stephen,
> 
> Can you help me to understand "#define MAX_CON_ID 16" in clkdev.c? I am trying
> to use clk_get() to acquire the clock with its name. This fails when the clock
> name is more than 15 characters. I traced it to this macro.
> 
> The reason of using clk_get() is I don't have device tree for my platform until
> device tree overlay is officially supported. So I use clkdev_add() in the clock
> driver.
> 
> So my issue is with the MAX_CON_ID. Is there a reason to limit it to 16?
> Wouldn't it be better to use kstrdup() in vclkdev_alloc()?
> 

Mike and I are not the maintainers of clkdev. The maintainer of
clkdev is Russell King.

I believe we can't use kstrdup() in vclkdev_alloc() because we
don't know if vclkdev_alloc() is called before the slab
allocators are up and running (this is why we have a
__clkdev_alloc() function). The simplest solution is to use
shorter names, can you do that?

-- 
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a Linux Foundation Collaborative Project

Re: What's the proper use of con_id in clkdev

[Russell King - ARM Linux]

On Tue, Oct 06, 2015 at 12:44:30PM -0700, Stephen Boyd wrote:
> On 10/05, York Sun wrote:
> > Michael and Stephen,
> > 
> > Can you help me to understand "#define MAX_CON_ID 16" in clkdev.c? I am trying
> > to use clk_get() to acquire the clock with its name. This fails when the clock
> > name is more than 15 characters. I traced it to this macro.
> > 
> > The reason of using clk_get() is I don't have device tree for my platform until
> > device tree overlay is officially supported. So I use clkdev_add() in the clock
> > driver.
> > 
> > So my issue is with the MAX_CON_ID. Is there a reason to limit it to 16?
> > Wouldn't it be better to use kstrdup() in vclkdev_alloc()?
> > 
> 
> Mike and I are not the maintainers of clkdev. The maintainer of
> clkdev is Russell King.
> 
> I believe we can't use kstrdup() in vclkdev_alloc() because we
> don't know if vclkdev_alloc() is called before the slab
> allocators are up and running (this is why we have a
> __clkdev_alloc() function). The simplest solution is to use
> shorter names, can you do that?

Why does anyone need a _connection_ _id_ longer than 15 characters
anyway?

It's not a system clock name - it's supposed to be a device _specific_
clock _input_ name.  This statement comes from many years experience,
where people have repeatedly passed clk_get(NULL, "global clock name")
and eventually run into great problems, ending up having to pass clk
connection names through platform data, or clk pointers through
platform data.  Both are abhorrent.

Use the API as it was designed to be used: always use
clk_get(device, "device-input-name") or clk_get_sys("device-name",
"device-input-name") and not clk_get(NULL, "global-clock-name").

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according to speedtest.net.

Re: What's the proper use of con_id in clkdev

[York Sun]

On 10/06/2015 12:50 PM, Russell King - ARM Linux wrote:
> On Tue, Oct 06, 2015 at 12:44:30PM -0700, Stephen Boyd wrote:
>> On 10/05, York Sun wrote:
>>> Michael and Stephen,
>>>
>>> Can you help me to understand "#define MAX_CON_ID 16" in clkdev.c? I am trying
>>> to use clk_get() to acquire the clock with its name. This fails when the clock
>>> name is more than 15 characters. I traced it to this macro.
>>>
>>> The reason of using clk_get() is I don't have device tree for my platform until
>>> device tree overlay is officially supported. So I use clkdev_add() in the clock
>>> driver.
>>>
>>> So my issue is with the MAX_CON_ID. Is there a reason to limit it to 16?
>>> Wouldn't it be better to use kstrdup() in vclkdev_alloc()?
>>>
>>
>> Mike and I are not the maintainers of clkdev. The maintainer of
>> clkdev is Russell King.
>>
>> I believe we can't use kstrdup() in vclkdev_alloc() because we
>> don't know if vclkdev_alloc() is called before the slab
>> allocators are up and running (this is why we have a
>> __clkdev_alloc() function). The simplest solution is to use
>> shorter names, can you do that?
> 
> Why does anyone need a _connection_ _id_ longer than 15 characters
> anyway?
> 
> It's not a system clock name - it's supposed to be a device _specific_
> clock _input_ name.  This statement comes from many years experience,
> where people have repeatedly passed clk_get(NULL, "global clock name")
> and eventually run into great problems, ending up having to pass clk
> connection names through platform data, or clk pointers through
> platform data.  Both are abhorrent.
> 
> Use the API as it was designed to be used: always use
> clk_get(device, "device-input-name") or clk_get_sys("device-name",
> "device-input-name") and not clk_get(NULL, "global-clock-name").
> 

Thanks to all for the guidance.

York