Message-ID: <5387F8EF.3030607@linaro.org>
Date:	Thu, 29 May 2014 22:20:15 -0500
From:	Alex Elder <elder@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>, mporter@...aro.org,
	bcm@...thebug.org, devicetree@...r.kernel.org
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] clk: bcm281xx: implement prerequisite clocks

On 05/23/2014 07:53 PM, Mike Turquette wrote:
> Quoting Alex Elder (2014-05-20 05:52:39)
>> @@ -743,11 +746,16 @@ struct clk *kona_clk_setup(struct kona_clk *bcm_clk)
>>         clk = clk_register(NULL, &bcm_clk->hw);
>>         if (IS_ERR(clk)) {
>>                 pr_err("%s: error registering clock %s (%ld)\n", __func__,
>> -                       init_data->name, PTR_ERR(clk));
>> +                       name, PTR_ERR(clk));
>>                 goto out_teardown;
>>         }
>>         BUG_ON(!clk);
>>  
>> +       /*  Make it so we can look the clock up using clk_find() */
> 
> s/clk_find/clk_get/ ?
> 
>> +       bcm_clk->cl.con_id = name;
>> +       bcm_clk->cl.clk = clk;
>> +       clkdev_add(&bcm_clk->cl);
> 
> This is not so nice. I'll explain more below.

OK, despite what I said before, I do need this, or
something like it, so I can look up clocks by name.
(Continued below.)

> 
>> +
>>         return clk;
>>  out_teardown:
>>         bcm_clk_teardown(bcm_clk);
>> diff --git a/drivers/clk/bcm/clk-kona.c b/drivers/clk/bcm/clk-kona.c
>> index d8a7f38..fd070d6 100644
>> --- a/drivers/clk/bcm/clk-kona.c
>> +++ b/drivers/clk/bcm/clk-kona.c
>> @@ -1195,6 +1195,48 @@ static bool __peri_clk_init(struct kona_clk *bcm_clk)
>>         return true;
>>  }
>>  
>> +static bool __kona_clk_init(struct kona_clk *bcm_clk);
>> +static bool __kona_prereq_init(struct kona_clk *bcm_clk)
>> +{
>> +       struct clk *clk;
>> +       struct clk_hw *hw;
>> +       struct kona_clk *prereq;
>> +
>> +       BUG_ON(clk_is_initialized(bcm_clk));
>> +
>> +       if (!bcm_clk->p.prereq)
>> +               return true;
>> +
>> +       clk = clk_get(NULL, bcm_clk->p.prereq);
> 
> The clkdev global namespace is getting polluted with all of these new
> prereq clocks. If there was an associated struct device *dev with them
> then it wouldn't be a problem, but you might get collisions with other
> clock drivers that also use NULL for the device.

Yes I recognize this.  Ideally a CCU would have a device struct
associated with it that I could use, because the name of a clock
is unique within that context.  But I have no such device available.
(Please correct me if I'm wrong.  I don't want to make one up, and
I would like to use it if it exists.)

> It would be a lot nicer for the clocks that require a prereq clock to
> just use clk_get(dev, "well_known_name"); in the same way that drivers
> use it, without considering it a special case.

I can do something like that if I can get a meaningful device
structure.  Do you have any suggestions?

Other than this issue, I've implemented all of the previous
initialization routines using ->prepare() instead, and it
works fine.  I'm going to send an updated series out tomorrow.
I want to look it over again after a good night's sleep...

					-Alex

>> +       if (IS_ERR(clk)) {
>> +               pr_err("%s: unable to get prereq clock %s for %s\n",
>> +                       __func__, bcm_clk->p.prereq, bcm_clk->init_data.name);
>> +               return false;
>> +       }
>> +       hw = __clk_get_hw(clk);
>> +       if (!hw) {
>> +               pr_err("%s: null hw pointer for clock %s\n", __func__,
>> +                       bcm_clk->init_data.name);
>> +               return false;
>> +       }
>> +       prereq = to_kona_clk(hw);
>> +       if (prereq->ccu != bcm_clk->ccu) {
>> +               pr_err("%s: prereq clock %s CCU different for clock %s\n",
>> +                       __func__, bcm_clk->p.prereq, bcm_clk->init_data.name);
>> +               return false;
>> +       }
>> +
>> +       /* Initialize the prerequisite clock first */
>> +       if (!__kona_clk_init(prereq)) {
>> +               pr_err("%s: failed to init prereq %s for clock %s\n",
>> +                       __func__, bcm_clk->p.prereq, bcm_clk->init_data.name);
>> +               return false;
>> +       }
>> +       bcm_clk->p.prereq_clk = clk;
> 
> The above seems like a lot effort to go to. Why not skip all of this and
> just implement the prerequisite logic in the .enable & .disable
> callbacks? E.g. your kona clk .enable callback would look like:
> 
> diff --git a/drivers/clk/bcm/clk-kona.c b/drivers/clk/bcm/clk-kona.c
> index d603c4e..51f35b4 100644
> --- a/drivers/clk/bcm/clk-kona.c
> +++ b/drivers/clk/bcm/clk-kona.c
> @@ -987,6 +987,12 @@ static int kona_peri_clk_enable(struct clk_hw *hw)
>  {
>  	struct kona_clk *bcm_clk = to_kona_clk(hw);
>  	struct bcm_clk_gate *gate = &bcm_clk->u.peri->gate;
> +	int ret;
> +
> +	hw->prereq_bus_clk = clk_get(hw->ccu, hw->prereq);
> +	ret = clk_enable(prereq_bus_clk);
> +	if (ret)
> +		return ret;
>  
>  	return clk_gate(bcm_clk->ccu, bcm_clk->init_data.name, gate, true);
>  }
> @@ -997,6 +1003,9 @@ static void kona_peri_clk_disable(struct clk_hw *hw)
>  	struct bcm_clk_gate *gate = &bcm_clk->u.peri->gate;
>  
>  	(void)clk_gate(bcm_clk->ccu, bcm_clk->init_data.name, gate, false);
> +
> +	clk_disable(hw->prereq_bus_clk);
> +	clk_put(hw->prereq_bus_clk);
>  }
>  
>  static int kona_peri_clk_is_enabled(struct clk_hw *hw)
> 
> 
> I guess it might take some trickery to get clk_get to work like that.
> Let me know if I've completely lost the plot.
> 
> Regards,
> Mike
> 

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