Re: [PATCH] clk: si5341: fix reported clk_rate when output divider is 2

From: Robert Hancock <robert.hancock@calian.com>
To: "sboyd@kernel.org" <sboyd@kernel.org>,
	"dev_public@wujek.eu" <dev_public@wujek.eu>,
	"mturquette@baylibre.com" <mturquette@baylibre.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-clk@vger.kernel.org" <linux-clk@vger.kernel.org>
Subject: Re: [PATCH] clk: si5341: fix reported clk_rate when output divider is 2
Date: Thu, 13 Jan 2022 22:29:41 +0000	[thread overview]
Message-ID: <d36fbe1176fd6182bd65c9a995fbf4614a112597.camel@calian.com> (raw)
In-Reply-To: <20220113212312.19D85C36AE3@smtp.kernel.org>

On Thu, 2022-01-13 at 13:23 -0800, Stephen Boyd wrote:
> +Robert
> 
> Please review
> 
> Quoting Adam Wujek (2021-12-03 06:12:07)
> > SI5341_OUT_CFG_RDIV_FORCE2 shall be checked first to distinguish whether
> > a divider for a given output is set to 2 (SI5341_OUT_CFG_RDIV_FORCE2
> > is set) or the output is disabled (SI5341_OUT_CFG_RDIV_FORCE2 not set,
> > SI5341_OUT_R_REG is set 0).
> > Before the change, divider set to 2 (SI5341_OUT_R_REG set to 0) was
> > interpreted as output is disabled.
> > 
> > Signed-off-by: Adam Wujek <dev_public@wujek.eu>
> > ---
> >  drivers/clk/clk-si5341.c | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/clk/clk-si5341.c b/drivers/clk/clk-si5341.c
> > index b7641abe6747..15b1c90cafe5 100644
> > --- a/drivers/clk/clk-si5341.c
> > +++ b/drivers/clk/clk-si5341.c
> > @@ -798,6 +798,15 @@ static unsigned long
> > si5341_output_clk_recalc_rate(struct clk_hw *hw,
> >         u32 r_divider;
> >         u8 r[3];
> > 
> > +       err = regmap_read(output->data->regmap,
> > +                       SI5341_OUT_CONFIG(output), &val);
> > +       if (err < 0)
> > +               return err;
> > +
> > +       /* If SI5341_OUT_CFG_RDIV_FORCE2 is set, r_divider is 2 */
> > +       if (val & SI5341_OUT_CFG_RDIV_FORCE2)
> > +               return parent_rate / 2;
> > +
> >         err = regmap_bulk_read(output->data->regmap,
> >                         SI5341_OUT_R_REG(output), r, 3);
> >         if (err < 0)
> > @@ -814,13 +823,6 @@ static unsigned long
> > si5341_output_clk_recalc_rate(struct clk_hw *hw,
> >         r_divider += 1;
> >         r_divider <<= 1;
> > 
> > -       err = regmap_read(output->data->regmap,
> > -                       SI5341_OUT_CONFIG(output), &val);
> > -       if (err < 0)
> > -               return err;
> > -
> > -       if (val & SI5341_OUT_CFG_RDIV_FORCE2)
> > -               r_divider = 2;
> > 
> >         return parent_rate / r_divider;
> >  }

Looks reasonable to me. I guess this bug doesn't affect register settings that
were previously applied by this driver, as it always sets the RDIV to 1 when
setting the FORCE2 flag, but if the chip has power-up NVM configuration
generated by ClockBuilder etc. then this problem could show up.

Reviewed-by: Robert Hancock <robert.hancock@calian.com>

-- 
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com