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

[Ryan Chen]

> -----Original Message-----
> From: Andrew Jeffery <andrew@xxxxxxxx>
> Sent: Friday, October 29, 2021 11:46 AM
> To: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>; Joel Stanley <joel@xxxxxxxxx>
> Cc: Michael Turquette <mturquette@xxxxxxxxxxxx>; Stephen Boyd
> <sboyd@xxxxxxxxxx>; linux-clk@xxxxxxxxxxxxxxx; Linux Kernel Mailing List
> <linux-kernel@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCHv3] clk:aspeed:Fix AST2600 hpll calculate formula
> 
> 
> 
> 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.

It would modify to following
	} else if (hwstrap & BIT(8)) {
> 
> >     /* CPU running at 1.6GHz */
> >     m = 0xBF;
> > } else {
> >    /* CPU running at 1.2Ghz */
> >    m = val  & 0x1fff;
> > }
> >
> >>