[PATCH v2 6/6] drm/bridge: cdns-mhdp8546: Fix the interrupt enable/disable

[Nikhil Devshatwar]

On 11:21-20201110, Tomi Valkeinen wrote:
> On 09/11/2020 19:06, Nikhil Devshatwar wrote:
> > When removing the tidss driver, there is a warning reported by
> > kernel about an unhandled interrupt for mhdp driver.
> > 
> > [   43.238895] irq 31: nobody cared (try booting with the "irqpoll" option)
> > ... [snipped backtrace]
> > [   43.330735] handlers:
> > [   43.333020] [<000000005367c4f9>] irq_default_primary_handler threaded [<000000007e02b601>]
> > cdns_mhdp_irq_handler [cdns_mhdp8546]
> > [   43.344607] Disabling IRQ #31
> > 
> > This happens because as part of cdns_mhdp_bridge_hpd_disable, driver tries
> > to disable the interrupts. While disabling the SW_EVENT interrupts,
> > it accidentally enables the MBOX interrupts, which are not handled by
> > the driver.
> > 
> > Fix this with a read-modify-write to update only required bits.
> > Do the same for enabling interrupts as well.
> > 
> > Signed-off-by: Nikhil Devshatwar <nikhil.nd at ti.com>
> > ---
> >  drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> > index 2cd809eed827..6beccd2a408e 100644
> > --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> > +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> > @@ -2146,7 +2146,8 @@ static void cdns_mhdp_bridge_hpd_enable(struct drm_bridge *bridge)
> >  
> >  	/* Enable SW event interrupts */
> >  	if (mhdp->bridge_attached)
> > -		writel(~(u32)CDNS_APB_INT_MASK_SW_EVENT_INT,
> > +		writel(readl(mhdp->regs + CDNS_APB_INT_MASK) &
> > +		       ~CDNS_APB_INT_MASK_SW_EVENT_INT,
> >  		       mhdp->regs + CDNS_APB_INT_MASK);
> >  }
> >  
> > @@ -2154,7 +2155,9 @@ static void cdns_mhdp_bridge_hpd_disable(struct drm_bridge *bridge)
> >  {
> >  	struct cdns_mhdp_device *mhdp = bridge_to_mhdp(bridge);
> >  
> > -	writel(CDNS_APB_INT_MASK_SW_EVENT_INT, mhdp->regs + CDNS_APB_INT_MASK);
> > +	writel(readl(mhdp->regs + CDNS_APB_INT_MASK) |
> > +	       CDNS_APB_INT_MASK_SW_EVENT_INT,
> > +	       mhdp->regs + CDNS_APB_INT_MASK);
> >  }
> >  
> >  static const struct drm_bridge_funcs cdns_mhdp_bridge_funcs = {
> 
> Good catch. I wonder why we need the above functions... We already enable and disable the interrupts
> when attaching/detaching the driver. And I think we want to get the interrupt even if we won't
> report HPD (but I think we always do report it), as we need the interrupts to track the link status.
> 

I read from the code that there is TODO for handling the mailbox
interrupts in the driver. Once that is supported, you will be able to
explictily enable/disable interrupts for SW_EVENTS (like hotplug) as
well as mailbox events. This enabling specific bits in the interrupt
status.


Nikhil D
>  Tomi
> 
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