[PATCH v3] ARM: Samsung SoC: clksrc-clk: wait for the stable SRC/DIV status.

[MyungJoo Ham]

On Mon, Aug 2, 2010 at 2:30 PM, Kukjin Kim <kgene.kim at samsung.com> wrote:
> MyungJoo Ham wrote:
>>
>> Many MUX and clock dividers have a status bit so that users can wait
>> until the status is stable. When corresponding registers are accessed
>> while a clock is not stable, we may suffer from unexpected errors.
>>
>> Therefore, we introduce a mechanism to let the operations related with
>> updating SRC/DIV registers of clksrc-clk wait for the stabilization:
>> clk_set_parent, clk_set_rate.
>>
>> In order to use this feature, the definition of clksrc_clk should
>> include reg_src_stable or reg_div_stable. With effective rec_src_stable
>> values, clk_set_parent returns with a stabilized SRC register and
>> with effective rec_div_stable values, clk_set_rate returns with a
>> stabilized DIV register. If .reg field is null, its (either SRC or DIV)
>> register's status is not checked and returned without waiting; i.e.,
>> some MUX/DIV may not need this feature.
>>
>> When setting reg_*_stable, .size is used to tell the value of "stable".
>> If .size = 0, the stable status is 0 and if .size = 1, the stable status
>> is 1.
>>
>> Signed-off-by: MyungJoo Ham <myungjoo.ham at samsung.com>
>> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
>> --
>> v2:
>>       - Wait-for-stable loop is described at an inline function.
>> v3:
>>       - Stop using clksrc_reg for stable bits. Use "clkstat_reg" for
>>         them.
>>
>> ---
>>  arch/arm/plat-samsung/clock-clksrc.c              |   14 +++++++++++++
>>  arch/arm/plat-samsung/include/plat/clock-clksrc.h |   22
>> +++++++++++++++++++++
>>  2 files changed, 36 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/plat-samsung/clock-clksrc.c
> b/arch/arm/plat-samsung/clock-
>> clksrc.c
>> index 46d204a..79ae92e 100644
>> --- a/arch/arm/plat-samsung/clock-clksrc.c
>> +++ b/arch/arm/plat-samsung/clock-clksrc.c
>> @@ -50,6 +50,15 @@ static unsigned long s3c_getrate_clksrc(struct clk
> *clk)
>>       return rate;
>>  }
>>
>> +static inline void s3c_wait_for_stable(struct clkstat_reg *stat)
>> +{
>> +     WARN_ON(stat == NULL);
>
> if (stat == NULL)
>        return;

Because .reg_*_stable is included in struct clksrc_clk and
s3c_wait_for_stable is called by clk_set_parent and clk_set_rate,
which have struct clksrc_clk, stat is unlikely to be NULL and if it's
NULL, s3c_wait_for_stable is called from a wrong function and wrong
context; thus, I'd use WARN for it rather than silently doing return.

>
> If don't need to check status, have not become define relevant status
> register.
>
>> +     if (stat->reg) {
>
> No need?...or need to check stat->reg and stat->shift?

If stat->reg is NULL (it can be intentionally NULL), it means that the
corresponding struct clksrc_clk does not have stable-stat bit; thus,
pass this checking routine. And, stat->shift may be both 0 and
positive effectively.

stat->reg = 0 : NO STAT REGISTER
stat->reg != 0 : STAT Register Exists. Use stat->shift to specify the
bit (stat->shift can be 0 or larger)

>
>> +             do { } while (((__raw_readl(stat->reg) >> stat->shift) & 1)
>> +                             != stat->stable);
>
> I'm still wondering we _really_ need 'stable'...just comments is enough,
> right now.

S5PV210 is fine without stable because stat->stable is always 0 for S5PV210.

However, this is for "Samsung-SoC" not for "S5PV210" although only
S5PV210 uses this feature for now.

I've added stat->stable for the generality. Would it be better discard
such generality and assume that other Samsung-SoC systems will also
use the same stat bit scheme for every register (0 for stable, 1 for
changing for every STAT register) with S5PV210? If we can guarantee
such homogeneousity, getting rid of stable property would be perfectly
fine. It is added just because I couldn't sure about Samsung-SoC chips
other than S5PV210. (and I thought some chips may use different scheme
for each register; e.g., some registers use 0 for stable, some others
use 1 for stable)

>
>> +             do { } while (((__raw_readl(stat->reg) >> stat->shift) & 1)
>> +                             != stat->stable);
>
>> +     }
>> +}
>> +
>>  static int s3c_setrate_clksrc(struct clk *clk, unsigned long rate)
>>  {
>>       struct clksrc_clk *sclk = to_clksrc(clk);
>> @@ -68,6 +77,8 @@ static int s3c_setrate_clksrc(struct clk *clk, unsigned
> long rate)
>>       val |= (div - 1) << sclk->reg_div.shift;
>>       __raw_writel(val, reg);
>>
>> +     s3c_wait_for_stable(&sclk->reg_div_stable);
>> +
>>       return 0;
>>  }
>>
>> @@ -93,6 +104,9 @@ static int s3c_setparent_clksrc(struct clk *clk, struct
> clk
>> *parent)
>>               clksrc |= src_nr << sclk->reg_src.shift;
>>
>>               __raw_writel(clksrc, sclk->reg_src.reg);
>> +
>> +             s3c_wait_for_stable(&sclk->reg_src_stable);
>> +
>>               return 0;
>>       }
>>
>> diff --git a/arch/arm/plat-samsung/include/plat/clock-clksrc.h
> b/arch/arm/plat-
>> samsung/include/plat/clock-clksrc.h
>> index 50a8ca7..f1d54da 100644
>> --- a/arch/arm/plat-samsung/include/plat/clock-clksrc.h
>> +++ b/arch/arm/plat-samsung/include/plat/clock-clksrc.h
>> @@ -40,11 +40,30 @@ struct clksrc_reg {
>>  };
>>
>>  /**
>> + * struct clkstat_reg - register definition for clock stat bits
>> + * @reg: pointer to the register in virtual memory.
>> + * @shift: the shift in bits to where the bitfield is.
>> + * @stable: the bit value of stable status.
>> + */
>> +struct clkstat_reg {
>> +     void __iomem            *reg;
>> +     unsigned short          shift;
>> +     unsigned short          stable;
>
> If you want to use this, just 'value' is better.
> But...I think...we don't need this field now.
>
>> +};
>> +
>> +/**
>>   * struct clksrc_clk - class of clock for newer style samsung devices.
>>   * @clk: the standard clock representation
>>   * @sources: the sources for this clock
>>   * @reg_src: the register definition for selecting the clock's source
>>   * @reg_div: the register definition for the clock's output divisor
>> + * @reg_src_stable: the register definition to probe if reg_src is
>> + *    stabilized after the update of reg_src. It is "stabilized" if
>> + *    reg[shift] == size. If reg == NULL, this stable reg is not looked
>> + *    up. Thus, in S5PV210, size is usually 0.
>> + * @reg_div_stable: the register definition to probe if reg_div is
>> + *    stabilized after the update of reg_div. Same mechanism with
>> + *    reg_src_stable.
>>   *
>>   * This clock implements the features required by the newer SoCs where
>>   * the standard clock block provides an input mux and a post-mux divisor
>> @@ -61,6 +80,9 @@ struct clksrc_clk {
>>
>>       struct clksrc_reg       reg_src;
>>       struct clksrc_reg       reg_div;
>> +
>> +     struct clkstat_reg      reg_src_stable;
>> +     struct clkstat_reg      reg_div_stable;
>>  };
>>
>>  /**
>> --
>
>
> Thanks.
>
> Best regards,
> Kgene.
> --
> Kukjin Kim <kgene.kim at samsung.com>, Senior Engineer,
> SW Solution Development Team, Samsung Electronics Co., Ltd.
>
>



-- 
MyungJoo Ham (함명주), Ph.D.
Mobile Software Platform Lab,
Digital Media and Communications (DMC) Business
Samsung Electronics
cell: 82-10-6714-2858