Re: [PATCHv3] clk:aspeed:Fix AST2600 hpll calculate formula

[Andrew Jeffery]

On Fri, 8 Oct 2021, at 18:02, Ryan Chen wrote:
>> -----Original Message-----
>> From: Joel Stanley <joel@xxxxxxxxx>
>> Sent: Friday, October 8, 2021 12:06 PM
>> To: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
>> Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>; Stephen Boyd
>> <sboyd@xxxxxxxxxx>; Andrew Jeffery <andrew@xxxxxxxx>;
>> linux-clk@xxxxxxxxxxxxxxx; Linux Kernel Mailing List
>> <linux-kernel@xxxxxxxxxxxxxxx>
>> Subject: Re: [PATCHv3] clk:aspeed:Fix AST2600 hpll calculate formula
>> 
>> On Sat, 25 Sept 2021 at 02:24, Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
>> wrote:
>> >
>> 
>> A few notes on process:
>> 
>> > v2 -> v3: change else than if to directly else if
>> > v1 -> v2: add Fixes commit hash
>> 
>> As this is normally information for reviewers to know what you've changed
>> since the last version, we normally put this below the --- in the patch, which
>> means it is not included in the commit message.
>> 
>> Also we put a space between the PATCH and v3 in the subject. If you use the
>> tools, it will generate this for you:
>> 
>> git format-patch -v3 -1 --to=...
>> 
>> >
>> > AST2600 HPLL calculate formula [SCU200] HPLL Numerator(M): have fixed
>> > value depend on SCU strap.
>> > M = SCU500[10] ? 0x5F : SCU500[8] ? 0xBF : SCU200[12:0]
>> 
>> I recommend adding to the commit message the text from my first review:
>> 
>> From the datasheet:
>> 
>> CPU frequency selection
>> 000 1.2GHz
>> 001 1.6GHz
>> 010 1.2GHz
>> 011 1.6GHz
>> 100 800MHz
>> 101 800MHz
>> 110 800MHz
>> 111 800MHz
>> 
>> So when the system is running at 800MHz or 1.6GHz, the value for the
>> numerator (m) in SCU204 is incorrect, and must be overridden.
>
> Yes, SCU204 will be overridden by chip design.
> Let me clarify m is in SCU200[12:0] not SCU204. SCU204 is NB not 
> related with freq.
>
>> 
>> >
>> > if SCU500[10] = 1, M=0x5F.
>> > else if SCU500[10]=0 & SCU500[8]=1, M=0xBF.
>> > others (SCU510[10]=0 and SCU510[8]=0)
>> > depend on SCU200[12:0] (default 0x8F) register setting.
>> >
>> > HPLL Denumerator (N) =  SCU200[18:13] (default 0x2)
>> > HPLL Divider (P)         =      SCU200[22:19] (default 0x0)
>> >
>> > Fixes: d3d04f6c330a ("clk: Add support for AST2600 SoC")
>> > Signed-off-by: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
>> > ---
>> >  drivers/clk/clk-ast2600.c | 28 +++++++++++++++++++++++++++-
>> >  1 file changed, 27 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/clk/clk-ast2600.c b/drivers/clk/clk-ast2600.c
>> > index 085d0a18b2b6..d30188355aaf 100644
>> > --- a/drivers/clk/clk-ast2600.c
>> > +++ b/drivers/clk/clk-ast2600.c
>> > @@ -169,6 +169,32 @@ static const struct clk_div_table
>> > ast2600_div_table[] = {  };
>> >
>> >  /* For hpll/dpll/epll/mpll */
>> > +static struct clk_hw *ast2600_calc_hpll(const char *name, u32 val) {
>> > +       unsigned int mult, div;
>> > +       u32 hwstrap = readl(scu_g6_base + ASPEED_G6_STRAP1);
>> > +
>> > +       if (val & BIT(24)) {
>> > +               /* Pass through mode */
>> > +               mult = div = 1;
>> > +       } else {
>> > +               /* F = 25Mhz * [(M + 2) / (n + 1)] / (p + 1) */
>> > +               u32 m = val  & 0x1fff;
>> > +               u32 n = (val >> 13) & 0x3f;
>> > +               u32 p = (val >> 19) & 0xf;
>> > +
>> 
>> Add a comment:
>> 
>> /* If the CPU is running at 800Mhz. */
>> 
>> > +               if (hwstrap & BIT(10))
>> > +                       m = 0x5F;
>> 
>> /* If the CPU is running at 1600Mhz. */
>> 
>> > +               else if (hwstrap & BIT(8))
>> > +                       m = 0xBF;
>> 
>> 
>> Or you could copy what I suggested in the first patch, and write it like this,
>> which I think is clear:
>> 
>> ff (hwstrap & BIT(10)) {
>>     /* CPU running at 800MHz */
>>    m = 95;
>> } else if (hwstrap & BIT(10)) {
>>     /* CPU running at 1.6GHz */
>>   m  = 191;
>> } else {
>>    /* CPU running at 1.2Ghz */
>>   m = val  & 0x1fff;
>> }
>
> How about following 
>
> ff (hwstrap & BIT(10)) {
>     /* CPU running at 800MHz */
>     m = 0x5F;
> } else if (hwstrap & BIT(10)) {

This is the same condition as the `if` above. That doesn't seem right.

>     /* CPU running at 1.6GHz */
>     m = 0xBF;
> } else {
>    /* CPU running at 1.2Ghz */
>    m = val  & 0x1fff;
> }
>
>>