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

[wlf]

Hi Heikoï

å 2016å11æ10æ 17:21, Heiko StÃbner åé:
> 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.
Thanks very much.
I will try to update a new patch.

Best regards,
         Wulf

> Heiko