On Wed, Jan 20, 2016 at 03:42:54PM +0100, Heiko Stuebner wrote:
> Commit e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1") removed
> the special ops struct for read-only clocks and instead opted to handle
> them regularly.
>
> On the rk3368 this results in breakage as aclkm now gets set a value.
> While it is the same divider, the A53 core still doesn't like it.
> The reason being that "ACLKENMasserts one clock cycle before the rising
> edge of ACLKM" and the clock should only be touched when STANDBYWFIL2
> is asserted.
>
> So make sure, read-only clocks don't touch the clock-register at all
> even if only writing the same value.
>
> Fixes: e6d5e7d90be9 ("clk-divider: Fix READ_ONLY when divider > 1")
> Reported-by: Zhang Qing <zhangqing at rock-chips.com>
> Signed-off-by: Heiko Stuebner <heiko at sntech.de>
It wouldn't hurt to clarify in the comment that this isn't just an
optimisation, and that even writing the same value to the hardware may
not be safe.
In any case
Reviewed-by: James Hogan <james.hogan at imgtec.com>
Cheers
James
> ---
> drivers/clk/clk-divider.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index ded3ff4..6dfe261 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -391,6 +391,10 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate,
> unsigned long flags = 0;
> u32 val;
>
> + /* don't do writes in read-only case */
> + if (divider->flags & CLK_DIVIDER_READ_ONLY)
> + return 0;
> +
> value = divider_get_val(rate, parent_rate, divider->table,
> divider->width, divider->flags);
>
> --
> 2.6.4
>
>
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