I know it has already been merged, but while doing some
clock investigations of the RPI3 I came accross this code:
> On 09.10.2015, at 03:37, Eric Anholt <e...@anholt.net> wrote:
> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> index dd295e4..8502a4b 100644
> --- a/drivers/clk/bcm/clk-bcm2835.c
> +++ b/drivers/clk/bcm/clk-bcm2835.c
> +static unsigned long bcm2835_pll_get_rate(struct clk_hw *hw,
> + unsigned long parent_rate)
> +{
> + struct bcm2835_pll *pll = container_of(hw, struct bcm2835_pll, hw);
> + struct bcm2835_cprman *cprman = pll->cprman;
> + const struct bcm2835_pll_data *data = pll->data;
> + u32 a2wctrl = cprman_read(cprman, data->a2w_ctrl_reg);
> + u32 ndiv, pdiv, fdiv;
> + bool using_prediv;
> +
> + if (parent_rate == 0)
> + return 0;
> +
> + fdiv = cprman_read(cprman, data->frac_reg) & A2W_PLL_FRAC_MASK;
> + ndiv = (a2wctrl & A2W_PLL_CTRL_NDIV_MASK) >> A2W_PLL_CTRL_NDIV_SHIFT;
> + pdiv = (a2wctrl & A2W_PLL_CTRL_PDIV_MASK) >> A2W_PLL_CTRL_PDIV_SHIFT;
> + using_prediv = cprman_read(cprman, data->ana_reg_base + 4) &
> + data->ana->fb_prediv_mask;
> +
> + if (using_prediv)
> + ndiv *= 2;
Is this really correct?
As far as I interpret the name “fb_predic_mask" it should be either:
pdiv * = 2; /* there is already a divider of 2 applied */
or
ndiv *= 2; /* we need to multiply bot integer and fractional by 2 */
fdiv *= 2;
As it is a pre-divider, I would assume it is the first,
but I could be wrong - not knowing a lot about PLLs.
Just want to raise this as a question.
Martin
