Re: [PATCH] phy: rockchip-inno-usb2: correct 480MHz output clock stable time

From: Heiko Stübner
Date: Thu Nov 10 2016 - 04:22:47 EST


Am Donnerstag, 10. November 2016, 10:54:49 schrieb wlf:
> Hi Doug,
>
> å 2016å11æ10æ 04:54, Doug Anderson åé:
> > Hi,
> >
> > On Mon, Nov 7, 2016 at 5:00 AM, William Wu <wulf@xxxxxxxxxxxxxx> wrote:
> >> We found that the system crashed due to 480MHz output clock of
> >> USB2 PHY was unstable after clock had been enabled by gpu module.
> >>
> >> Theoretically, 1 millisecond is a critical value for 480MHz
> >> output clock stable time, so we try to change the delay time
> >> to 1.2 millisecond to avoid this issue.
> >>
> >> Signed-off-by: William Wu <wulf@xxxxxxxxxxxxxx>
> >> ---
> >>
> >> drivers/phy/phy-rockchip-inno-usb2.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/phy/phy-rockchip-inno-usb2.c
> >> b/drivers/phy/phy-rockchip-inno-usb2.c index ecfd7d1..8f2d2b6 100644
> >> --- a/drivers/phy/phy-rockchip-inno-usb2.c
> >> +++ b/drivers/phy/phy-rockchip-inno-usb2.c
> >> @@ -267,7 +267,7 @@ static int rockchip_usb2phy_clk480m_enable(struct
> >> clk_hw *hw)>>
> >> return ret;
> >>
> >> /* waitting for the clk become stable */
> >>
> >> - mdelay(1);
> >> + udelay(1200);
> >
> > Several people who have seen this patch have expressed concern that a
> > 1.2 ms delay is pretty long for something that's supposed to be
> > "atomic" like a clk_enable(). Consider that someone might call
> > clk_enable() while interrupts are disabled and that a 1.2 ms interrupt
> > latency is not so great.
> >
> > It seems like this clock should be moved to be enabled in "prepare"
> > and the "enable" should be a no-op. This is a functionality change,
> > but I don't think there are any real users for this clock at the
> > moment so it should be fine.
> >
> > (of course, the 1 ms latency that existed before this patch was still
> > pretty bad, but ...)
>
> Thanks a lot for your suggestion.
> I agree with you. clk_enable() will call spin_lock_irqsave() to disable
> interrupt, and we add
> more than 1ms in clk_enable may cause big latency.
>
> And according to clk_prepare() description:
> In a simple case, clk_prepare can be used instead of clk_enable to
> ungate a clk if the
> operation may sleep. One example is a clk which is accessed over I2c.
>
> So maybe we can remove the clock to clk_prepare.
>
> Hi Heiko, Frank,
> What do you think of it?

moving to clk_prepare sounds sensible. That way you can switch from delay to
sleep functions as well.


Heiko