On Thu, 08 Feb 2018 15:20:16 +0000 Eric Anholt eric@anholt.net wrote:

Boris Brezillon boris.brezillon@bootlin.com writes:

...

All bcm2835 PLLs should be gated before their rate can be changed. Setting CLK_SET_RATE_GATE will let the core enforce that, but this is not enough to make the code work in all situations. Indeed, the CLK_SET_RATE_GATE flag prevents a user from changing the rate while the clock is enabled, but this check only guarantees there's no Linux users. In our case, the clock might have been enabled by the bootloader/FW, and, because we have CLK_IGNORE_UNUSED set, Linux never disables the PLL. So we have to make sure the PLL is actually disabled before changing the rate.

Fixes: 41691b8862e2 ("clk: bcm2835: Add support for programming the audio domain clocks") Cc: stable@vger.kernel.org Signed-off-by: Boris Brezillon boris.brezillon@bootlin.com

---

drivers/clk/bcm/clk-bcm2835.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c index 6c5d4a8e426c..051ce769c109 100644 --- a/drivers/clk/bcm/clk-bcm2835.c +++ b/drivers/clk/bcm/clk-bcm2835.c @@ -678,6 +678,18 @@ static int bcm2835_pll_set_rate(struct clk_hw *hw, u32 ana[4]; int i;

• /*

• * Normally, the CLK_SET_RATE_GATE flag prevents a user from changing
  

• * the rate while the clock is enabled, but this check only makes sure
  

• * there's no Linux users.
  

• * In our case, the clock might have been enabled by the bootloader/FW,
  

• * and, since CLK_IGNORE_UNUSED flag is set, Linux never disables it.
  

• * So we have to make sure the clk is actually disabled before changing
  

• * the rate.
  

• */
  

• if (bcm2835_pll_is_on(hw))

• bcm2835_pll_off(hw);
  

I'm not sure this improves the situation. If the PLL was on, then presumably there's a divider using it and a CM clock using that, so we'll probably end up driving some glitches on them.

Hm, yes, but if someone is trying to change the rate of the PLL, and the core doesn't know other clks depend on this PLL (which is the case if we reach this point), we're already in big trouble.

Does the common clk framework have a way to disable unused clocks from the leaf clocks up to this root, before the general disable-unused-clocks path happens late in the boot process?

Not that I know of. What do you have in mind?