RE: [PATCH 1/1] clk:aspeed:Fix AST2600 hpll calculate formula

[Ryan Chen]

> -----Original Message-----
> From: Joel Stanley <joel@xxxxxxxxx>
> Sent: Wednesday, September 1, 2021 2:49 PM
> To: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
> Cc: BMC-SW <BMC-SW@xxxxxxxxxxxxxx>; Michael Turquette
> <mturquette@xxxxxxxxxxxx>; Stephen Boyd <sboyd@xxxxxxxxxx>; Andrew
> Jeffery <andrew@xxxxxxxx>; linux-clk@xxxxxxxxxxxxxxx; Linux Kernel Mailing List
> <linux-kernel@xxxxxxxxxxxxxxx>
> Subject: Re: [PATCH 1/1] clk:aspeed:Fix AST2600 hpll calculate formula
> 
> Hello Ryan,
> 
> Thanks for the patch. I have some questions about it below.
> 
> On Wed, 18 Aug 2021 at 08:05, Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
> wrote:
> >
> > 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 see 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?
> 
M is in SCU200 not SCU204.
The patch code is point out the issue, that not only check the SCU200 to calculate the hpll, 
but also need check the SCU500[10] and SCU510[8], it will effect the M value.

> > 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)
> 
> Is this the case for all revisions of the soc, from A0 through to A3?
Yes. it is.
> 
> Do you have a datasheet update that captures this information?
No.
> 
> When you resend, please add a fixes line as follows, as this code has been
> present since we introduced the driver:
Thanks a lot.
> 
> Fixes: d3d04f6c330a ("clk: Add support for AST2600 SoC")
> 
> >
> > Signed-off-by: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>
> > ---
> >  drivers/clk/clk-ast2600.c | 29 ++++++++++++++++++++++++++++-
> >  1 file changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clk/clk-ast2600.c b/drivers/clk/clk-ast2600.c
> > index 085d0a18b2b6..5d8c46bcf237 100644
> > --- a/drivers/clk/clk-ast2600.c
> > +++ b/drivers/clk/clk-ast2600.c
> > @@ -169,6 +169,33 @@ static const struct clk_div_table
> > ast2600_div_table[] = {  };
> >
> >  /* For hpll/dpll/epll/mpll */
> 
> This comment needs to stay with ast2600_calc_pll, and just drop hpll from the
> list.
> 
> > +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;
> > +
> > +               if (hwstrap & BIT(10))
> 
> So this is testing if the CPU is running at 800Mhz.
> 
> > +                       m = 0x5F;
> > +               else {
> > +                       if (hwstrap & BIT(8))
> 
> And this is testing if the CPU is running at 1.6GHz.
> 
> I would write it like this:
> 
> u32 m;
> 
> if (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;
> }
> 
> Cheers,
> 
> Joel