Hi David,
On Mon, 15 Dec 2014 13:34:56 +0000
David Laight <David.Laight@xxxxxxxxxx> wrote:
> From: Sergei Shtylyov
> > Hello.
> >
> > On 12/15/2014 4:03 PM, Boris Brezillon wrote:
> >
> > > Avoid interpreting useless status flags when we're not waiting for such
> > > events by masking the status variable with the interrupt enabled register
> > > value.
> >
> > > Reported-by: Patrice VILCHEZ <patrice.vilchez@xxxxxxxxx>
> > > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
> > > ---
> > > drivers/usb/gadget/udc/atmel_usba_udc.c | 6 +++++-
> > > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > > diff --git a/drivers/usb/gadget/udc/atmel_usba_udc.c b/drivers/usb/gadget/udc/atmel_usba_udc.c
> > > index 55c8dde..bc3a532 100644
> > > --- a/drivers/usb/gadget/udc/atmel_usba_udc.c
> > > +++ b/drivers/usb/gadget/udc/atmel_usba_udc.c
> > > @@ -1612,12 +1612,14 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
> > >
> > > spin_lock(&udc->lock);
> > >
> > > - status = usba_readl(udc, INT_STA);
> > > + status = usba_readl(udc, INT_STA) & usba_readl(udc, INT_ENB);
> > > DBG(DBG_INT, "irq, status=%#08x\n", status);
> > >
> > > if (status & USBA_DET_SUSPEND) {
> > > toggle_bias(udc, 0);
> > > usba_writel(udc, INT_CLR, USBA_DET_SUSPEND);
> > > + usba_writel(udc, INT_ENB,
> > > + usba_readl(udc, INT_ENB) | USBA_WAKE_UP);
> > > udc->bias_pulse_needed = true;
> > > DBG(DBG_BUS, "Suspend detected\n");
> > > if (udc->gadget.speed != USB_SPEED_UNKNOWN
> > > @@ -1631,6 +1633,8 @@ static irqreturn_t usba_udc_irq(int irq, void *devid)
> > > if (status & USBA_WAKE_UP) {
> > > toggle_bias(udc, 1);
> > > usba_writel(udc, INT_CLR, USBA_WAKE_UP);
> > > + usba_writel(udc, INT_ENB,
> > > + usba_readl(udc, INT_ENB) & ~USBA_WAKE_UP);
> > > DBG(DBG_BUS, "Wake Up CPU detected\n");
> > > }
> >
> > Looks like t make sense to read the INT_ENB register into a separate
> > variable, to save on extra reads?
>
>
> Better still remember the written value in one of the structures so
> that it doesn't have to be read at all.
Hmm, I'm getting back to this suggestion.
While I definitely understand why I should use a local variable to
store INT_ENB value in usba_udc_irq, I don't see the point of mirroring
INT_EN status in an udc struct field (after all, INT_EN will always
contain the value we previously set).
Is this a performance concern ?
Regards,
Boris
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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