On Thu, 08 Feb 2018 15:15:42 +0000
Eric Anholt <eric@xxxxxxxxxx> wrote:
> Boris Brezillon <boris.brezillon@xxxxxxxxxxx> writes:
>
> > In order to enable a PLL, not only the PLL has to be powered up and
> > locked, but you also have to de-assert the reset signal. The last part
> > was missing. Add it so PLLs that were not enabled by the FW/bootloader
> > can be enabled from Linux.
> >
> > Fixes: 41691b8862e2 ("clk: bcm2835: Add support for programming the audio domain clocks")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>
> > ---
> > drivers/clk/bcm/clk-bcm2835.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> > index a07f6451694a..6c5d4a8e426c 100644
> > --- a/drivers/clk/bcm/clk-bcm2835.c
> > +++ b/drivers/clk/bcm/clk-bcm2835.c
> > @@ -602,6 +602,9 @@ static void bcm2835_pll_off(struct clk_hw *hw)
> > const struct bcm2835_pll_data *data = pll->data;
> >
> > spin_lock(&cprman->regs_lock);
> > + cprman_write(cprman, data->a2w_ctrl_reg,
> > + cprman_read(cprman, data->a2w_ctrl_reg) &
> > + ~A2W_PLL_CTRL_PRST_DISABLE);
> > cprman_write(cprman, data->cm_ctrl_reg,
> > cprman_read(cprman, data->cm_ctrl_reg) |
> > CM_PLL_ANARST);
>
> For turning off, the FW just does the equivalent of:
>
> cprman_write(cprman, data->cm_ctrl_reg, CM_PLL_ANARST);
> cprman_write(cprman, data->a2w_ctrl_reg, A2W_PLL_CTRL_PWRDN);
Hm, the write to ->a2w_ctrl_reg overwrites the
NDIV/PDIV values done in bcm2835_pll_set_rate(). So, either we do:
cprman_write(cprman, data->cm_ctrl_reg, CM_PLL_ANARST);
cprman_write(cprman, data->a2w_ctrl_reg,
cprman_read(cprman, data->a2w_ctrl_reg) |
A2W_PLL_CTRL_PWRDN);
or we cache the pdiv/ndiv values in struct bcm2835_pll and only apply
them in bcm2835_pll_on().
I'd recommend going for the former to keep the changes easily
backportable to older kernels.
>
> How about we do that, instead?
>
> > @@ -640,6 +643,10 @@ static int bcm2835_pll_on(struct clk_hw *hw)
> > cpu_relax();
> > }
> >
> > + cprman_write(cprman, data->a2w_ctrl_reg,
> > + cprman_read(cprman, data->a2w_ctrl_reg) |
> > + A2W_PLL_CTRL_PRST_DISABLE);
> > +
> > return 0;
> > }
>
> I agree with this hunk -- they drop PRST at the very end, after lock.
--
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
http://bootlin.com